If we look back to the European history, it seems incredible how many intelligent and rational people embraced the irrational doctrine about the extermination of the Jewish people. It is irrational, because we cannot imagine a psychologically sane man willing the death of somebody else, without being in a direct conflict.
The intelligent and rational people use to care much for their reputation, because their words hardly can be heard, if they have not a respectable name in society. Thus, perhaps they believed that it was a menace to their dignity to defend a population which was publicly revealed by the political propaganda and public opinion as a despicable category of people.
Meanwhile, the less intelligent persons are easily lured by political propaganda especially when it spreads tough ideas, among which are the irrational ones, since the rational ones bore the people with their complicated reasons.
The rebirth of a similar irrational doctrine about the extermination or at least the expulsion of Muslims seems incredible after the past experience of Holocaust. We cannot imagine that the most intelligent and rational persons from the Western countries will find justifiable such a doctrine. However, they have already found sufficient reasons in the public space for being afraid of not losing their reputation if they defend the rights of the Muslim population, as it is, for instance, the right of building mosques in the Western cities.
A powerful political propaganda against Muslims could be sufficient for making the intelligent and rational people to forget all the irrationality they discovered in the previous genocides of Jewish people.