I don't think they're actually lying about their beliefs. At least not in a traditional sense of the word. Fascist leaders are as full of shit as any other bourgeois politician but I find it unlikely that everyone's racist uncle is deliberately weaving a web of lies to conceal his true power level. That is simply too much effort to put into it.

It is more likely that they actually believe what they say they believe, even though it is completely internally contradictory. They have a more or less conscious conviction that they ought to enjoy status and privilege above those who are not like them and as a consequence they gravitate towards adopting whatever position that advances this conviction because it feels good to them.

I don't know if there's much use for this kind of psychoanalysis but at least to me this is yet another argument why trying to talk reason to fascists is futile. They did not arrive at their fascism through reasoning but rather through gut feelings and half-realised opportunism.