The marching morons has a lot to answer for, really, since variations on this is an idea that crops up like weed,

This is kind of an relevant argument because it means this - despite my non-political phrasing - is really a political topic because the opinion coalition effects are possibly much stronger than any solid predictions to be had. Or to rephrase this: Any actual biological effect is outweight by memetic effects.

it is a pretty absurd scenario.

I beg to differ.