I did not say it is illegitimate; in fact I happen to think that there are several parallels between the rise of Hitler in 1930’s and the rise of Putin in 2000’s. I simply would prefer to talk in less inflammatory terms, because any time someone brings up Hitler the result is that Hitler is discussed, rather than the initial subject.
I remember comparing the rise of, not Putin, but Obama to the rise of Hitler and commenting on the parallels. But I did so only after a careful reservation of the scope and intent of the comparison to avoid the problems you describe.