"It is an intellectually shallow way to argue."<quoted text>
I think it is a fallacy to compare anyone to Hitler or Nazis in the first place. It is an intellectually shallow way to argue.
However, when Christians try to argue that Hitler was not a Christian it is just as intellectually dishonest. We know that he claimed to be Catholic and that he used Biblical language and talked of God. We do not know what he truly believed, but that is true of anyone you care to name.
I remember some goofhead on this thread arguing for multiple pages that the Nazis were caused by Charles Darwin. On another thread some idiots have argued that pro-choice folks are like Hitler.
It is dumb as balls to compare people to Hitler because frankly it is just an easy target. He's universally considered to be a symbol of evil so if you want to vilify someone completely you might think of comparing them to Hitler. Don't do it. You'll lose the argument in a split second.
If someone did not claim to be a nazi, someone would not bring it up. Best to have all facts before making a judgement, it is an intellectually shallow thing to do.