@rawr-monster and @eyestumblin asked me to elaborate so here goes:
Death Note is a show with a very clear central premise: no one should have the power to kill others without consequence. Not the cops, not corporations, not the Mob, not civilians, no one.
Even outside of the 2000s-era criticisms of the Japanese justice system, even if you're looking at it in a vacuum, Death Note makes it incredibly obvious what it's trying to say. It starts this off by making it very clear, right out of the gate, that the audience identification character really, really should not have this power.
For Death Note's original target audience, Light is everything you're supposed to be. He's smart, diligent, good-looking, athletic, popular but not too popular. He's The Perfect Middle-Class Japanese Teenage Boy. If you're the kind of edgy, smart Japanese teenage boy who would want to watch an anime supernatural crime drama in the mid-00s? Light is built for you to imprint on like a baby duckling.
...And then the show goes out of its way to point out, in the first proper story arc, that Light is the villain of this piece. From the introduction of L to the end of the Raye Penber/Naomi Misora arc, the show makes it very, very clear that Light is a hypocrite with a massive ego. Sure, he says that he's only killing criminals to make a better world. Sure, maybe he panicked and killed fake-L in self-defense. Sure, maybe the life of Reye Penber and any law enforcement chasing Kira were worth the clear drop in the crime rate. Maybe.
But then Light kills one of the very few unambiguously Good members of the Death Note cast, does so in a smug and cruel way, and the entire scene is framed as tragic in a way that none of the criminal deaths really were. The whole world goes quiet. And Naomi Misora stumbles off to commit suicide. By the end of that arc, even if you'd otherwise be sympathetic to Light- even if you're still rooting for him to get away with it- it's a lot harder to justify what he's doing. He's not just breaking a few eggs to make an omelet- at this point, he's actively happy to kill anyone who gets in his way.
So. Okay. The Perfect Japanese Teenage Boy (TM) can't be trusted with the power to kill indiscriminately. Maybe the problem is just that Light, as a person, is an asshole with impure motives, and if you gave the Death Note to someone who's a better person, you'd be better off. Maybe you could find someone who's motivated by love, and they'd do a better job with that power.
Everyone, say hello to Misa Amane, who is utterly driven by love and devotion, and probably one of the crazier/more evil characters on the show! She'd do anything, no matter how terrible, just because Light told her to do it. She is utterly without remorse, utterly without fear, and utterly driven by a darkly Romantic fanaticism.
Light gets to dodge what's coming to him twice because of Misa and love- once because Misa's love for Light lets him start the Yotsuba arc, and once because Rem's love for Misa becomes a diabola ex machina. In the world of Death Note, love is not a pure enough motive to let you kill indiscriminately - in fact, it makes you worse.
Okay, well, (our hypothetical edgy teenage viewer might say), cLEARLY the problem is that everyone here is too emotional, and you need to be able to detach from the situation to use the power of life and death. Of course you'd kill indiscriminately if you've got feeeeelings about it, but someone who is driven by Logic and Reason? Surely they'd never do anything wrong.
...And then L gets his hands on the Death Note, and immediately starts trying to figure out how to use it to prove that some of the rules in the Death Note are fake and Light is guilty. L's plan is to have a criminal on death row write in the Death Note and wait the 13 days to see if he dies. It's simple. Logical. Effective. It's also extremely reminiscent of the stuff Kira's been doing this entire time, and the implication is that, had L lived longer and used the Note more, he might become No Different.
(I think it's significant that in The Movie, L uses the Death Note exactly once, with himself as the victim, and he turns down the Death Note when it's offered to him. TheMovie!L is an unambiguously heroic character, and therefore, he will not kill without consequences.)
The power to kill without any consequence to yourself corrupts you. It makes you want to use it to solve more and more of your problems. It turns you into a fucking monster, one name at a time. And nothing can stop that process except refusing to use that power. Love cannot shield you. Rationality cannot shield you. Justice cannot shield you.
And every other character who gets the Death Note reinforces that theme. The Yotsuba Group? Big corporations should not get to kill without consequences. Mello? Criminals/genius detectives should not get to kill without consequence. Mikami? The Perfect Japanese Adult is outright sadistic about how he uses the Death Note. And on, and on, and on.
Near outright tells Light, in their final confrontation: "You are a murderer, and this notebook is the worst weapon of mass murder in the world." Using the Death Note is not justice; it's not going to bring about a perfect new world. It's murder, full stop. Light has become a mass murderer, a monster, by killing over and over again.
Death Note has a theme: no one should be allowed to kill without consequences, because it makes you a monster. It is not subtle about that theme. It is very, very blatant, and the only way it could be more blatant is if Near stopped to deliver an Atlas-Shrugged-style monologue about it.
and so seeing people reduce that to 'haha ACAB' gets my goat, because no. No, it's not just ACAB. anyone with the power to kill indiscriminately and without consequence- whether it's a cop, a megacorp, an autistic supergenius, a mob boss, or a perfect audience-insert- would become A Bastard.
this is a show that makes it abundantly clear that there is Symbolism and it has a Point, in the way that only stuff aimed at teenagers that's trying to be Deep can do. how you get through the entirety of Death Note and walk away with "there's no point! a cop's son decides to be the worst person ever! Light is Uniquely Terrible and that's all there is to it!" is fucking beyond me.
