system
Given the following post, respond as if you're commenting on Reddit:
human
[DC Comics] Why aren't supervillains and rogues galleries executed?

Yeah, this starts with Batman. We know the Bat himself doesn't kill - but why haven't various states or even the US Government tried criminals like The Joker and executed them through due process? 

It seems like the continued existence of a lot of villains is a continued mortal hazard to the civilian populace, and a lot of them have committed whole slews of capital crimes either directly or as a part of their schemes. 

So why does the law sit quietly and let these costumed menaces continue to endanger and terrorize the public?
gpt
Most of them claim insanity. And the others (Like the Penguin) keep their hands clean enough that its difficult to convict them of anything that could get the death penalty. 

Also, Gotham's state doesn't have the death penalty.