That's an opinion(so of course it can't be wrong) that I have heard, it is being debated fairly intelligently downthread along with a debate about the fantastic King of the Hill and Office Space.
Here is a list of movies that critics and non-critics consider to be much better post WWII satires than Idiocracy, according to internet ratings of these movies. Note: many of these are more humorous and brutal while being less crude and light-hearted than Idiocracy. Also many have plot, emotion, and deep characterization.
Films: American Psycho, A Clockwork Orange, Fahrenheit 451, Nineteen Eighty-Four, Dr. Strangelove, Office Space(also Mike Judge)
http://en.wikipedia.org/wiki/Satire
My main problem with Idiocracy as a satire is that the message it sends is flatly incorrect, because the rules of their world are not the same as ours. It is a satire of some alternate universe in which we are not living, it has no applicability for the world we live in.
Film's message: "If our societies ever end up giving a competitive advantage to low IQ people, time travel will be necessary to correct society's decline."
The truth:"If our societies ever end up giving a competitive advantage to low IQ people, natural selection will take care of it, since intelligence seems to be a competitive advantage for apes."
I think the true message is also a better call to arms for both intelligent people and unintelligent people. The movie Idiocracy seemed like it was made to be consumed by the citizens of the low-IQ world, in both plot and acting. I do enjoy its light-heartedness.
Much more realistic are the famous dystopian texts, especially Harrison Bergeron: http://en.wikipedia.org/wiki/Harrison_Bergeron