Light Yagami certainly has a reputation among the fandom, and that reputation isn't founded for pointlessly. The justice-toting boy-genius murdered thousands of people, most of which without so much as batting an eye. And he doesn't regret a single one. On the contrary, he probably views each as a job well done. It isn't just the killing, either. Light claims each victim with boyish enthusiasm and possesses a childish demeanor that leads him to be competitive to the point of taunting the condemned with a sinister smile and dancing on their grave (literally, if he gets worked up enough). Yes, that's the Light Yagami we know, our unforgettable protagonist of Death Note.
Light is a killer. Light has no disturbed childhood to blame. Light voluntarily kills and once he found the Death Note, probably wouldn't be happy doing anything else. On those facts alone, we could infer any number of similar conclusions. I've heard Light called, by the morally concerned, disturbed. The face of evil. Hopelessly insane. And, most common of all, sociopath. The label insinuates a total lack of everything we call humanity. The inability to feel guilt for any wrongdoing, and thus, a total lack of conscience. If we chose to conclude that, then Light Yagami isn't normal, he isn't like you or me.
But the aforementioned facts are not all there is to Light Yagami, and it's a slam to the complexity - and, I emphatically insist, realism - of his character to assume as such merely because he kills. 'Killer' and 'sociopath' are not interchangable words. The nature of the killing has to be taken into considerion. As far as the victim is concerned, murder is murder is murder, but not as far as the perpetrator is. The immediate fact of the matter is that sociopaths are, as a rule, self-focused and unable to empathize with the world or the people around him. This contradicts the very nature of Kira's legacy. Certainly there's the fact that Light was a bored, underchallenged genius in a society where he functioned solely on outward appearances and achievements, and certainly there's no doubt that a part of Light was perhaps waiting for the opportunity to test himself. But I honestly cannot conceive how this in any way discounts the fact that the reason Light took the opportunity he did was out of his zealous sense of idealism.
We know for a fact that Light has a societal conscience, beyond mere conditioning (if that were the case, Light wouldn't posess even half the passion that he does). The first chapter/first episode of the series is exclusively about Light's convictions. First, the shock at perhaps having actually taken a person's life, and then the total horror when he's tested it again and realized that he's killed people and yes, it's his fault. The anxiety he feels, that he's capable of feeling, does inexcusably deny him from the title of sociopath. Light is so disturbed by his actions that he can't eat, can't sleep, loses ten pounds in the first week and looks as though he's about to throw up. And finally, the resolution: doing this could make the world a better place. "Even if I sacrifice my mind and soul," Light states (even predicts). "The world is rotting. Someone has to do it." Light even acts initially under the impression that a Shinigami is going to come take his soul as soon as he's found, and when Ryuk arrives he's surprised that he's not going to be punished. Agree with his methods or not, it wouldn't be wrong to call Light's ambition selfless, wanting to "protect the weak" and "make a perfect world" without, as far as the text writes, asking in return for anything conventional such as money, sex, or political power (which also separates him from being a dictator, by definition).
Some argue the sincerity of Light's resolve as being only an excuse to jump at the chance to ease his boredom. I don't personally think that's fair, but nonetheless, the very fact that Light experiences such vivid anxiety before impulsively engaging in such risky behavior already excludes him from the title.
Now to get technical. "Sociopath" isn't a medical term, and though it has general uses it's not a proper diagnosis. When talking about sociopaths/psychopaths in the psychology field, most often we're talking about Antisocial Personality Disorder. The brief definition as listed in the DSM-IV is "The essential feature for the diagnosis is a pervasive pattern of disregard for, and violation of, the rights of others that begins in childhood or early adolescence and continues into adulthood." Sure, that's pretty vague and by that sentence alone, I'd agree without a doubt that Light is quick to violate the human rights of others, in particular the right to life (but let it be stated that the same can be said of L, Near and Mello). But the criteria goes beyong that. First, we can't quite call Light an APD at the beginning of the series - one has to be an adult aged at least 18. Furthermore, APDs ought to have a history of conduct disorder (breaking the law, inappropriate actions, truancy, running away from home, etc) since before the age of 15. I think it's safe to say that the Yagami's golden boy who so emphatically values the law hasn't even come close. Also, APDs are known for drug and alcohol abuse, which again, does not apply.
Now to the actual criteria.
1. Failure to conform to social norms with respect to lawful behaviors as indicated by repeatedly performing acts that are grounds for arrest;
2. Deceitfulness, as indicated by repeatedly lying, use of aliases, or conning others for personal profit or pleasure;
3. Impulsivity or failure to plan ahead;
4. Irritability and aggressiveness, as indicated by repeated physical fights or assaults;
5. Reckless disregard for safety of self or others;
6. Consistent irresponsibility, as indicated by repeated failure to sustain consistent work behavior or honor financial obligations;
7. Lack of remorse, as indicated by being indifferent to or rationalizing having hurt, mistreated, or stolen from another.
1. Light absolutely does conform to social norms and takes great pains to do so. And he has the utmost respect for the law - in fact, he created Kira in order to encourage others to uphold the law. Yes, murder does happen to be grounds for arrest, but with vigilante idealism in mind, we have to examine the circumstances. Nor does Light, to my memory, ever break the law in the series unless it specifically pertains to his goal of "making the world a better place". We don't see him raping, stealing, anything of the sort - and instd of acting indifferent toward such thing, he shows his disdain by declaring war against them.
2. Absolutely Light's a liar and deceitful to the max. He's able to act charming and naturally likable by everyone around him, while secretly manipulating them for his goals. But the critera would qualify if only Light's intent while lying was for the purpose of personal profit or pleasure. Unless we claim that Light is Kira only because he wants to have godlike power over other people, which defeats the purpose of his 'perfect, crime-free utopia' as a supposed goal, then there is nothing personal about his reasons. Lying and manipulaing out of what he deems necessity for the survival of his ideal can't be placed on the same level as lying because he can, and he wants something tangible out of it.
3. This is hugely characteristic of a sociopath, and Light "Ten Steps Ahead" Yagami would greatly resent being told he's impulsive. To disclaim, Light is perfectly capable of making impulsive, thoughtless decisions - the impetuous murder of Lind L. Tailor is the primary example here. But it's important not to alienate the facts, and examine Light from the perspective of a 17 year old boy before we try to apply him to abnormal psychology. If this is one of the few times that Light acts recklessly without considering the consequences, then he's still doing better than most male adolescents. In fact, I try to imagine another teenage boy finding the Death Note, and using it to kill the people he doesn't like without realizing that he could be caught, so we have to give Light credit for usually thinking things through.
4. Light's cool and collected by nature, and what irritability he expresses is stress induced from the mind-consuming task of delivering justice while dodging every policing organization in the world. Light's not prone to physical aggression either, at least not abnormally so. The only person he initiates fighting with is L, and I would be reluctant to call that anything other than male testosterone in all its dysfunctional glory.
5. Disregard for safety of self and others? Very possibly. He's willing to sacrifice others in a heartbeat if it means maintaining Kira's reign. He even puts himself in very risky positions, such as revealing himself to Naomi, letting himself be incarcerated by L, arranging to be stood up by an armed drug addict on a bus, and, which I think takes the cake, standing right behind Raye Penber and threatening him in the flesh. It'd be incorrect to say that Light doesn't have guts. But the problem I have with the actual criteria here is that the actions aren't reckless. They're well-planned to the best of Light's ability. He spends plenty of time contemplating absolutely every tiny detail.
6. We have no reason to believe that Light is irresponsible. Despite being Kira, Light ensures that he performs all of his duties to the best of his abilities. He takes time to study, get into a prestigious university, go to work, diligently manage his relationships. This in no way applies to Light.
7. Finally, the main concern many raise about Light: his lack of remorse. I agree, Light does not feel remorse for any of his victims (with the possible exception of the first two). Nor does Light often express humanly concern for other people in general. Yet, again, there's situational factors to take into consideration. Light is a vigilante. With every fiber of his being, he believes that he's doing the right thing. He could even be compared to a soldier fighting some war against an evil, intangible force like terrorism. If he's killing for righteous reasons, the fact that he has no regrets is far different from a serial killer who has just made a hobby of slicing up innocents. A sociopath/ASP person may know that their actions are wrong from conditioning and textbook definitions, but they just wouldn't care, wouldn't be capable of caring. Contrarily, a vigilante believes he's doing the right thing and cares about doing the right thing - whether or not we morally assess the cause and agree is irrelevant. I would also like to bring up the vital nature of Light's murders. The fact that he kills by writing down a name in a notebook makes the murder method totally detached. He doesn't have to be there in front of his victim, which makes it significantly different from killing with a knife or a gun. Light's mentality while killing may be no different than the mentality of a teenage boy playing a video game - it lacks the harsh, griddy realism that should be the process of taking another human's life. And if he's just a kid knocking off the baddies in the comfort of his room with his metaphorical controller, the Death Note, how can he feel remorse?
In order to succeed as Kira and ultimately create his perfect, sinless utopia, Light knew from the start that he would have to be willing to sacrifice everything and everyone for this greater cause. In addition to his own "mind and soul", as he put, he had to be able to kill even a loved one with hardly a moment's notice. Some accuse Light of being selfish in that he'd let others die before himself - though on one hand, I most certainly agree, but to look at it from his perspective, if he dies, Kira dies with him. Again, Kira is worth more than any one person because Kira is the collective hope of the entire world. For this reason, I do think that Light did deliberately cram his feelings into some tiny cavern of his brain to not be bothered, and thus becomes cold and calculating throughout the series - until the startling contrast of losing his memories of Kira, in which a caring, noble-hearted Light appears who is at the opposite end of the spectrum - no goal is worth moral sacrifice. Amnesia!Light also prove that Light is capable of valuing others. Unlike a sociopath, who simply cannot.
Not to mention that, feelings pushed aside or not, Kira!Light does care about people. Ohba deliberately states in HTR13 that Light not only loves his family, but even has friends and cares about humanity as a whole. Is this demonstrated in the manga? There is a lot of debate over whether or not Light's performance at Soichiro's death was sincere or acted (I happen to think it's a twisted mixture of both) but there is one person in the series whom Light is unable to sacrifice, even knowing the consequences (which he knew were dire, and proved to be, ultimately becoming a major contribution to his downfall): Sayu Yagami. Light is seen helping his sister with her homework from the beginning of the series, taking the time to be with her even though he could have just as easily shut her away. Not to mention Sayu is extremely fond of him, too. During arc 2, Sayu is kidnapped by Mello's mafia gang. Light's shock at this announcement isn't merely surprise. He says her name with shaky uncertainty, now weighed with the decision: to give in to the kidnapper's demands and relinquish a precious Death Note, or to kill his sister and eliminate any leeway they might have on her. In the end, Light cannot bring himself to do it. Sure, he makes an excuse about the murder's trail may point to him, but this is feeble in comparison to the risk of giving the Death Note to the enemy. Not only is this a risk because with a Death Note in criminal hands, it can only be imagined what havoc could possibly occur, but also with another willing group to test the Death Note, any number of discoveries could be found (including the 13 day rule, or about the Shinigami, etc... crucial information that Mello does ascertain and give to Near). Light's intelligent enough to know this. But Light can't kill Sayu.
Would I diagnose Light with any personality disorders? I don't feel quite confident that Light's arrogant enough to be considered for Narcissistic Personality Disorder. He certainly thinks he's special (believing that the Death Note came to him for a purpose, that Ryuk chose him, that only he can be Kira), he's exploitative of others.. but does he require excessive admiration, or is it simply given? Is he that arrogant, or is he just cognizant of how exceptionally capable he actually is? Personally, I've always thought that Light suffered from depression prior to picking up the Death Note, part of which made him so vulnerable toward it, but that's an essay for another day.