The last time I taught Economic History, I enjoined my students to avoid using Hitler and the Nazis as rhetorical devices because such comparisons are almost always irrelevant. If you're talking about Stalin, Mao, and democide, then Hitler comparisons might be appropriate. If you're debating the merits of a vegetarian diet, then invoking Hitler's vegetarianism lends nothing to the debate. Here's Barney Frank dismissing such a comparison in the context of the health care debate; I ultimately think that reductio ad Hitlerum arguments will ultimately weaken the impact of the opposition to President Obama's health care proposals.