It's not like multiple rapists, child rapists, killers have been put in jail, got out and starting doing it again almost immediately IRL.
At some point, fiction is only a mild caricature of what happens in real life.
A convicted rapist will get life if he rapes again. How many times did the Joker re-commit crimes? And that's ignoring the sheer scale of their gruesome deeds.
Old-fashioned hero principles only mean that you're okay with more victims.