It is slow as molasses, but taking the high road may still help in the long run. Calling people racists, even if it's true, is effectively arguing by going "fuck you", which does nothing but further distance the two groups.
Let's say a racist family gets in an argument with a single guy who's a minority on the street. The racist parents are getting in the guy's face, while the guy is trying to be nice and reasonable.
Sure, the guy probably isn't going to get through to the parents of the family because those parents have probably been racist for decades and one conversation isn't going to sway them. But what about the kids in that family watching the argument? What if they've been told that minorities are scum their whole lives, but here they are seeing a minority acting way more reasonably than their parents currently are? Being nice has just planted the seed of doubt in those kids' heads, making them think that maybe minorities aren't the horrible beings that their parents keep saying they are. Maybe these kids will be more likely to hang out with minorities at school because of it. Maybe these kids won't grow up to be racists like their parents. That's the difference.
Now, what if the guy instead turned around and started yelling back at the parents in front of those kids, calling them racists and other names? Even if the anger is justified and the names are accurate (which they are), that behavior is confirming to the whole family that minorities are enemies and should be approached with caution. To the kids watching, that enforces the racial lines that their parents were drawing for them. It increases the chances of them growing up to be racists themselves.
