alt Hacker Newsbecause intelligence is mostly genetically-determined
None of the points of Idiocracy depend on whether intelligence is by nature or by nurture. The premise of the movie stays exactly the same if you replace those two minutes of backstory with a dysfunctional education system, the return of child labour, an increase in teen pregnancies, and anti-intellectualism in general.
I think the opening scene makes the hereditary position very clear, I don’t know how anyone could interpret that as not marking the case of ‘nature’ determining intelligence.
Edit; sorry, either I misread your comment or it was changed. On the premise that ignoring the intro a nurture based idiocracy could be possible, I would suggest it’s the thoroughness and extent of dumbing down that wouldn’t be possible if it was based on nurture.