What if you're a white person who thinks whites are getting a raw deal, but you're NOT a "neo-Nazi" or a Hitler-worshipper?
Most white advocates seek a general right of group self-determination that at most involves non-involvement with other racial groups, especially coercive involvement. Forced busing, affirmative action, immigration and non-discrimination laws are all examples of coercion that are opposed by white advocates.
In other words, they wish to simply decline the demands of other racial groups. That's "supremacy"? That's like calling a woman who refuses a man's sexual advances a "female supremacist.