I understood the society that Heinlein was trying to convey in Starship Troopers and A Moon Is a Harsh Mistress, but I also see they're completely impossible. The notion that they're militaristic or fascist is the most logical jump people make in order to make the society fit in with reality. It's a disconnect that breaks suspension of belief, so in order to restore the suspension of belief people's brain makes the connection to systems of governance that do fit. This is pretty much the only thing that turns me off reading more Heinlein.
I'll grant you that the society depicted in SST was, in many ways, rather incredible (as in "not credible"), but I always found the society depicted The Moon Is a Harsh Mistress rather credible, given the circumstances it happened in. I mean the "We either make this work, or we all die"-angle on the whole thing, makes it more credible than the SST society.