The Nazi's weren't terrorists (which is not to say that they didn't use terror to maintain control). But terrorism, in the classic political sense, is a tactic used by groups on the outside against the established power structure. In the case of the Nazis, they were the established power structure.

So if you're looking for a parallel to the Nazis, look to today's right-wing demagogues. And, yes, there is an object lesson in the way German Catholics went along. The mistake they made was in accepting the notion that because the regime was elected into power, it must be benign. 

They didn't learn otherwise until it was too late. The question is, will we repeat their error?