More seriously, while being racist towards white people is bad on its own merits, either as a violation of justice - judging someone for the actions of another - or on more Utilitarian grounds, most of the people that are seriously racist against the whities aren’t going to accept those arguments.
Thus the appeal to something they might actually care about.
It’s possible to create political will out of thin air, but a lot of the time it’s in reaction to historical or material factors, and political will with those factors will have deeper roots.
It’s important to realize along with this, that most politics will occur around the margins - whether groups of white supremacists are growing or shrinking, whether swing voters shift from one party to another, and so on. Strong believers do have an effect, but it’s necessary to have raw power mass at your disposal.
As such, the question is not about “but if we be nice to our rivals, they will still be maximally evil,” but about “what’s the marginal rate that people will enter or leave our enemy’s coalition?”
Now that doesn’t mean playing along nicely all the time, but for goodness sake people should be very careful and specific in who they are targetting, and most racism is really bad at doing that.
