Exactly. Hence my "boy who cried Wolf" comparison.

I think we're agreeing, but I'm also saying that it's been used to imply evil so long that it has lost meaning as an actual, historical example. One could easily say, "He endorses federal PSAs, like Hitler," and people would think you're against PSAs rather than just noting a historical fact. It sets the tone as automatically hostile. Hostile people, in politics, tend towards bias. Nobody wants to listen to them (unless they share the bias). It is ineffective to make the comparison in nearly all cases.