> Do you think that a 3rd party should be able to judge and ban you at will for something that you say in a group chat when everyone else in said group chat is fine with it?

Yes. If I were running Discord and learned that there was some Klan group advocating hate against black people, I'd shut it down – even if everyone in that chat was fine with the discussion.

It wouldn't be beneficial to me to have my platform be a host for that content, and it's not beneficial to society for me to facilitate hateful people easily connecting with each other.