To mark the tenth anniversary of Death Note, there's a fabulous analysis of the manga's protagonist over on Anime News Network.
Under the heading Ten Years of Death Note: Is Light the Bad Guy?, columnist Jacob Hope Chapman takes a reasonably in-depth, albeit whistle-stop look not only at the character of Light Yagami himself, but how fans received him and how the author may have intended him to be.
There's a discussion on why people might accept mass murder and even justify the need - touching upon the darker impulses within us all; and whether insanity runs more rampant than merely with Kira.
Chapman brilliantly, and humorously, makes the case for Light Yagami being no 'anti-hero' nor erstwhile saviour, but a villain par excellence. Perhaps manga's most iconic villain at that.
Though he never elaborates upon the point, the columnist does demonstrate quite clearly how easily society will accept the wicked and insane, if the justification is presented gradually and enticingly enough. In this regard using Kira apologists amongst the Death Note fandom as an example, rather than, say, Donald Trump's supporters. Seen from a long view, their pro-Kira arguments are denigrated as 'commonly insane'. Can't argue there!
Everyman Matsuda - The Reader's Representative Within the Death Note Plot?
Chapman also talks about other characters in relation to Light Yagami (who is, after all, the focus of his analysis).
In particular he notes how Matsuda is too regularly dismissed as merely the idiot of the Death Note world. When, upon closer inspection, it turns out that the young police officer holds a vital role within the narrative and its dramatis personæ.
Matsuda serves as an everyman, the character whose views act as a litmus test for the wider perspective of fashionable society. As he wavers in support of Kira, then so do the greater Japanese masses.
If not an actual bellwether, then Matsuda certainly performs as a weathercock, testing the winds of public acclaim or disdain concerning Kira at any given juncture.
Matsuda's emotional breakdown is one of the best parts of the show's finale because it just feels so right. Over time, without anyone noticing, Matsuda came to represent the everykid: all those normal Japanese millennials just trying to live their lives, maybe secretly posting defenses of Kira online, maybe just keeping their conflicted feelings to themselves, but open enough to the incredible change Kira had caused to feel like maybe condemning him wasn't fair. Of course there's something attractive about the idea of people who hurt others getting universally punished to create a more peaceful humanity. But it's just an idea, and when Matsuda is confronted with the reality of Kira—an egomaniacal brat who even killed his own dad to further his self-righteous empire—he feels more betrayed than anyone else.
~ Ten Years of Death Note: Is Light the Bad Guy?, Jacob Hope Chapman, Anime News Network (March 18th 2016)
Then we too, like Matsuda, get to retrace our own allegiances back through each worsening compromise to that first loosening of all common sense and good morals.
Instead, Chapman sees in Matsuda a proxy for Tsugumi Ohba's own secret views on the matter, which itself makes fascinating reading and compelling food for thought. It's definitely worth the time to check it out.