American History X isn't aimed at the worst sorts of bigots, from what I've heard a lot of them completely miss the point of it. Instead, it's aimed at non-extremist people who might find themselves slipping into hatred of some kind, be it against a minority for racist reasons, or a whole nation or culture due to nationalist reasons. Hate is something that only gets worse the more you feed it and that's what you see with Derick's character. He doesn't change until he finally comes to the realization that his hate has consumed him and destroyed his life and that of his family for no gain whatsoever. That's the central message of the movie, and you don't need to be a KKK member to get some value out of that message.

Similarly, I don't expect that the documentary Jihad Rehab will ever magically make a terrorist see the error of his ways, or that the movie Walking Up Dead will make a committed transphobe gay person see how wrong they've been. That's ok. But perhaps both films can ignite discussion among those who never knew of these issues or make them reflect on some of their own failings. Of course, no one has to watch these if they don't want to, but I find it a bit absurd if someone says they won't see it because they don't agree with the views of the protagonist.