"If you agreed with that, and it turned out Hitler said it(*) would that imply that you agreed with Hitler on any broader issues?"
It proves how Hitler tricked the Germans, does it not?
I presume you are referring back to the earlier quoted statement, rather than the hypothetical one I posited?
It does, which is why it should raise caution flags. The fact that someone proposes or agrees with a very bad idea, however, does not imply that the individual is a bad person. Many people agree with very evil notions because they are too naïve to see how evil they are. Only if someone is wantonly indifferent to the evils of the ideas they support should they be judged as being evil themselves.