Whu?

There is literally no eugenics in Idiocracy.

Eugenics = forced attempts to modify the genome since at least the times of ancient Greece via infanticide, murdering or sterilizing 'low quality' groups, paying desired groups to have more children, to modern literal selective breeding via government body mandates in Nazi eugenics etc.

New eugenics / 'liberal eugenics' = informed choice via technology eg scanning for downs syndrome in embryos and allowing parents the informed choice of termination, genome editing, etc. Which we are clearly not talking about within context, but also is not present or suggested in Idiocracy.

What doesn't fit into any definition of eugenics is telling people "hey if only the dumb people keep breeding, that will not end well".