It took this second thread for me to remember the SF story The Marching Morons by Cyril Kornbluth (1951 story).(someone posted on FR there is a similar movie plot by someone else).
Part of story synopsis——
People of higher intelligence often chose to have few children (or no children at all) for pragmatic reasons, while people of lower intelligence, compelled by their sex drives, had larger families and reproduced in greater numbers.
The simple-minded morons cannot be left to govern themselves or else the world will descend into chaos and war.
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Then the higher IQ people have to take care of the dumb ones and run everything for them.
So one thing they elites did for the low IQ people was have cars that could never go very fast. The speedometers would say 60 or 80 mph but the real speed was 15 or 25 mph. The drivers would be thrilled they were going fast.
That’s also the storyline for Idiocracy, a Hollywood box office flop nearly a quarter of a century ago! I laughed my ass of when I finally got my hands on a copy!