In restaurants I worked in a long time ago, servers would just call black people "Canadians" -- for instance, "Nope, don't sit those Canadians in my section, they don't tip."

Good luck filtering for stuff like that. And even if you did, people would just come up with new version.

Re: The core problem... Why would having extreme right wingers use your site even be a problem? Presumably extreme left wingers are okay?