Idiocracy's mechanism isn't as solid as it seems though even if high educated people do tend to have have less kid. The movie basically suggests "smart people have smart kids, dumb people have dumb kids, repeat forever." But you'd expect kids of very high or very low IQ parents to land closer to average in general. The "compounding" thing the movie relies on isn't really how it works in life.

And even if the premise of Idiocracy were true, less intelligent people aren't worth less than more intelligent people. That's the "eugenics-y vibe" problem mentioned earlier that makes the movie uncomfortable for some people.