Nowhere in the movie is that even hinted at.

The opening scene tells the viewer the decline in intelligence in the future is due to the less educated/intelligent reproducing more, that’s getting rather close to eugenics.

I don’t think this was intended as more than just a handwave argument as an explanation for the plot necessary premise of people being stupid in the future (i.e. it’s not something to get offended over) but it is mentioned nonetheless.

Freight Train by Alan Jackson (different to the other songs titled Freight Train that I’ve seen linked so far)