It's wrong to say no one else does. Your all or nothing approach falls flat out of the gate.
Either way, based on what you're implying, whites should continue to vote for the GOP because of self interest, since all other groups band together to vote against them. If the white self interest was exclusive, that's a bad thing, but then other minority self interest that's exclusive gets a wavier because of soccer mom style nannying and fear of being labeled a racist for fair play.