Yes, there's someone who I otherwise have a great respect for who has 'no x, y, or z clients' rules.
Having heard some of the stories, I can understand why they do it, but it still makes me a bit uncomfortable and I'd be happier with something like 'x, y and z clients have to make an extra effort to prove they're not assholes like some others in those categories, sorry'.
But ultimately it comes back to the same thought that everyone has their own boundaries, even if other people don't agree with them.