One, metal icons do not speak for metal. In fact, no one really does. Two, Napalm Death were a bunch of fucking Commies. Does that mean metal is against Capitalism or pro-Communism? Racism, pro or con, is part of the metal scene. That is just a given. Take sexism for example. Metal is riddled with misogynistic references, à la the virgin sacrifice or fucking prostitutes, whatever. So, metal is sexist, right? Does that mean metal needs to clean up its act and stop portraying these things in a "positive" light? What about violence in general? I suppose metal needs to stop being so unkind to others. Metal deals with subjects that most do not want to touch, and often approaches them in un-PC ways / alternative ways of thinking. Racism is certainly one of those subjects, as the Pantera and black metal acts you have just cited point out. Thus, racism is certainly a part of metal, as it should be.