Did you think Light was the hero when you watched it the first time? He's a teenage kid who suddenly gets way too much power, thoroughly abuses it, then starts killing innocents to avoid the consequences of his own actions. Even if his first few kills were literal supervillains, there is no justice in a world where Light decides who lives or dies.

Your idea of a revolutionary undermining the system is also an interesting story idea, but it's a very different story idea.