Everyone always jumps to eugenics to explain Idiocracy, but I don't ever remember hearing genetics mentioned in the movie. The movie merely states that dumb adults raise dumb children. I don't know about you, but I see that everyday. This doesn't need to be explained by genetics. Children mimic the ways the adults in their lives act to model themselves on as they mature. You can counter this with things like public education or community involvement, but if the parents are involved and interact with their child, they're going to mimic them. If you know a smart person who was raised by dumb people, chances are the parents weren't really involved with the kid as they grew up.

This isn't even a obscure fact. What do you think those Jesus Camps are for? Why do you think rich people send their kids to elite schools?