I have no doubt you're a good hearted person and have not made any assumptions to the contrary, but it does read as if you are chilled by a request for evidence that reason and truth are the best means of combating racial purity ideologies.
It would certainly be nice to rely on reason and truth if those strategies are indeed reliable. But the extant question is what if they're not?
The historical record suggests that appeals to reason, truth, and morality actually have a really terrible record as practical responses to autocracy. As we've been talking about Nazis, it's an easily verifiable fact that there was abundant intellectual, political, and religious opposition to their ideology and that none of these proved especially effective.
Once the nazis got comfortable and installed their people in key administrative positions, they just started arresting people whose public behavior was politically inconvenient for them. I don't want to start drawing parallels with individual current events which is more likely to confuse than to inform, but they're not hard to imagine.