From time to time I have used the term useful idiots to describe some folks. This is not a term I invented, though it's not clear who did.
Juan Cole this week behaved like a perfect useful idiot. This fellow could easily qualify.
I first really understood the term, however, when I read The Passing of an Illusion: The Idea of Communism in the Twentieth Century, by Francois Furet. Fortunately, Norman Geras has recently posted a fine review by Jeffrey Herf. He has me convinced that someday I should go read the book a second time because I seem to have missed all sorts of interesting things the first time.