There was an article I read a while ago about why Joker as Batman’s nemesis is overrated. I can’t remember where I found it now, but I remember the main ideas of it. Basically, Joker’s gimmick is old and tired. His rivalry with Batman has become forced. Batman’s character has grown and changed over the years, and the Joker no longer has any personal relevance to his story. Thematically, and narratively, it just doesn’t make sense to keep trying to make him Batman’s main enemy.
As for the people who take inspiration from Joker and commit crimes, I don’t think that they will go away if the Joker goes away. But the thing about Joker is that he’s a terrorist. He’s like the school shooters who callously end countless lives just for attention, and just because they can. But those kinds of people need a platform. Their effect is strongest when their thinking and ideas are being spread. So how do you deal with that? You don’t give them attention. And the Joker as a character gives those ideas a voice. We talk a lot about how representation in art and media is important, but that goes both ways. There’s the positive kind of representation, when there are more diverse casts of characters with POC and other groups being portrayed respectfully, but there is also the kind of representation that the Joker provides. People don’t suddenly become serial killers just because they read a comic with the Joker in it, they still have the basis for it, but seeing someone like the Joker express his opinions also gives them liscence to act on their own opinions. It lets them believe their thinking is valid. And if that can be stopped, it should be.
TLDR: DC should just let Jason kill the Joker.