It’s not like there are dozens of people In DC who can kill Joker, if something goes wrong, unlike in My Hero where Deku admitted he had no plans about how to ‘save’ Shigaraki and that he was the only person powerful enough in the entire planet who could beat him at that point, and outright put the entire world at risk, to help the mass murderer.
Also not like Deku outright admitted that he would kill if he needed to, but then decided to switch his mind, unlike Batman outright stating he has a no kill rule.