From Robinson's "Rah, rah, RAH!":

(Note: all these are most-brainless, as not one of the critics is in any position to know anything about Heinlein the man. The man they attack is the one they infer from his fiction: a mug's game.)

(1) "Heinlein is a fascist." This is the most popular Heinlein shibboleth in fandom, particularly among the young and, of course, exclusively among the ignorant. I seldom bother to reply, but in this instance I am being paid. Dear sir or madam: kindly go to the library, look up the dictionary definition of fascism. For good measure, read the history of fascism, asking the librarian to help you with any big words. Then read the works of Robert Heinlein, as you have plainly not done yet. If out of forty-two books you can produce one shred of evidence that Heinlein—or any of his protagonists—is a fascist, I'll eat my copy of Heinlein in Dimension.

If you don't own a copy of it, you can find the entire essay here.