I've never actually gone looking for threads on this subject but from the OP's initial post I assume its a bit of a contentious issue?
Personally I have no problems with a WG stating who she won't see and I don't feel the need for a reason why either. I just put it down to a matter of personal preference.
I for example don't see women more than a couple of years older than myself (exception being made on Wednesday though) nor do I see black WG's. Tried it once, really nice, attractive, friendly girl but sexually didn't do it for me so I shan't go back for a second try.
The only time I take objection is when their particularly rude about it or outright racist over the matter.
Afraid I couldn't see an "interracial" tab being effective though, it would have to be specifically tailored to suit particular race options i.e. African, Arabic, European... Way to many variables involved. Much easier for the WG to just politely decline to see certain groups that she does not enjoy the company of.... A "no chavs" tab on the other hand would work a treat