Re-writing this whole comment because I can do better.

There was a lot of things that got me to stop being a chud. HBomberguy dunking on Davis Aurini was a big one. But realy the biggest factor was the realization that basically all my friends could be categorized as 'undesireables' and everyone who held the kinds of beliefs I was being fed (i.e. the people it was 'acceptible' for me to hang out with) just rubbed me the wrong way.

That was mostly an internal journey, though, and not what you'd call replicable. A better option would be to show them that their boogeymen are not only stupid (e.g. 'diversity quotas' are basically unenforceable) but actively dangerous (e.g. abandoning the push for diversity would lead to an underclass of minorities ripe for even worse exploitation). Unless they genuinely have no sense of empathy, explaining how their perfect society requires thousands of people (including lots of people they might like) to be put to death