I guess the question being asked here is whether those Hitler supporters acting so violently should affect your decision on whether to support Hitler or not. Rationally speaking, it should not, because his supporters and the man himself are two separate things, but the initial response will likely be to assign both things to the same category and have both be affected by the negative perception of the supporters.

I think if you use examples that are less confrontational or biased you can get the message across better. Hitler is usually not a useful subject for examples or comparisons.

I'm pretty sure I actually saw this in a philosophy textbook, which would mean there are likely observations or studies on the subject.