There's obviously different lines in the sand for different people, but this attitude always strikes me as stupid.
A vtuber is more than just a character, it is the person behind the vtuber. I've made an analogy with Kevin Spacey before; yeah I'll watch Kevin Spacey movies and be fine with it because it is purely a character that he's playing, but I'm not going to watch Kevin Spacey playing video games and talking about his day, he's a disgusting person so why would I want to listen to him?
So, for some people that line may be a one year old trans pride tweet, for others it might be IRL pedophilia and rape, etc. but if someone has NO line on what they find acceptable on a basic humanity/morality level as long as it's off stream, I greatly question their conscience (if they have one).