It has been raised to my attention that in the Glossary for Prejudice one of the listed items is "political view" should not be a protected class. It should be okay to disallow someone from participating because of their well known hard-line prejudices even if they 'are on their best behaviour' and don't show active discrimination in the group itself.

The best example for this is the 'Nazi Bar' anecdote:

"you have to nip it in the bud immediately. These guys come in and it's always a nice, polite one. And you serve them because you don't want to cause a scene. And then they become a regular and after awhile they bring a friend. And that dude is cool too.

And then THEY bring friends and the friends bring friends and they stop being cool and then you realize, oh shit, this is a Nazi bar now. And it's too late because they're entrenched and if you try to kick them out, they cause a PROBLEM. So you have to shut them down.