> The white supremacist see the world differently and they view different power structures than you do.
And evolution deniers may view the world differently, too, but as the law must address a certain social reality, it aspires to be based on empirical observation, rather than on personal views. After those observations have been made, the law is, of course, based on personal values. For example, it is an empirical fact that blacks have been marginalized from American society, but it is a question of personal values (as well as empirical questions of expected efficacy) whether or not affirmative action should be made.
> So while you might focus on one type of power structure they focus on another.
No, they simply do not know what power structure is. As far as I know, there is little empirical scholarship by white supremacists.
> In a way that has always felt racist to me: A black person cannot really think white people are subhuman, because white people are obviously not...
Again, you are shifting the discussion to subjective thought, while the law is mostly concerned with objective effects. I don't know what some person may or may not think, neither do I care (as a legislator). I do care about the effect actions have, and because of the existing power structure in society, actions by different people have different effects.
BTW, there is a very interesting debate in legal theory -- which also has to do with studies about the different values on the left and on the right -- precisely about that. Some claim that conservatives are more concerned with actions, while liberals are more concerned with effects. This is not just a matter of values, but also of consequences (where applying the first system has conservative consequences, i.e., it turns to preserve the current social structure). Most legal systems vary on this matter from one law to another, and even judgment practices may change over time. One can most certainly claim that legal systems, including Twitter's rules, should be based on actions more than on effect, but I think that in recent decades, the West has shifted more towards to effect-oriented view, where an action is judged based on its context and its harm.