It's odd that in 2014 so much political debate is still about Hitler. Was Napoleon still so prominent in people's minds almost 70 years after his downfall? Nonetheless, I recommend as interesting and generally persuasive this piece "Hitler wasn't a socialist. Stop saying he was," by Tim Stanley at The Telegraph, written in response to "Leftists become incandescent when reminded of the socialist roots of Nazism," by Daniel Hannan. I weighed in on a similar issue a few years ago with my FrumForum piece "Yes, James Von Brunn Is Right Wing." The Nazis/fascists-are-socialists-are-liberals argument is a reaction to, but no smarter than, the conservatives-are-Nazis/fascists argument (and I recall being called a fascist at least once in college for being a libertarian conservative; now that I'm a centrist, I suppose I could be called that from either side). Right and left in politics are cumbersome but not useless terms. I'd apply left to those who think they represent some advance from a benighted past, and right to those who draw more on the past (often an idealized past). Granted, that doesn't readily capture the environmentalist/socialist who exalts preindustrial, precapitalist society, or the libertarian transhumanist who wants to upload his (or, more rarely, her) mind into a computer, but it at least moves us away from the they-started-it insult-fest of which they're-like-Hitler is but one part.
Note: this post initially was titled Reduction ad Hitlerum, for which I blame spell check.