This makes sense when you consider the fact that getting elected to Congress is not easy -- hence members are likely to be significantly more intelligent than average. Given a fairly high prior on human hypocrisy to begin with, combined with the severely diminishing social returns on overtly displaying intelligence, hypocrisy is almost always a better explanation for recognizably "idiotic" congressional behavior than actual idiocy.

(This is not to say that Congress is especially competent; but their true incompetence tends to be of the sort common to many groups of people -- the kind that later explains failures, rather than the kind that would make them the object of contemporary derision .)