What stuck me particularly was how extremely obviously stupid it was, that was what made it so disappointing as a villain motivation. It broke the sort of immersion of the story because it immediately made me start thinking about how ill-educated and/or irrational Thanos would have to be to believe that, and then, when none of these "genius" characters attempted to point this out to him (you'd have thought someone hard-nosed like Tony Stark would have at a dead minimum)
Even more effective if one of the characters who doesn't play the "smartest guy in the room" card to point it out - like, if Ant-man or Cap turns to Tony and goes, "Wait, isn't that dumb? The population's just going to bounce back eventually, right?" and Tony says, "Yeah, in like 70 years. His plan is pointless! ... Hey, purple guy, do you know your plan is pointless, or do you just not like to think that hard?"
When I first heard it, I genuinely instantly expected someone to attempt to talk some sense into him, to say "In a hundred years you'll just need to snap again!", and maybe we'd eventually get a revelation that the faux-Malthusian logic was just a smokescreen
Well, since we are talking about writers being dumb, let us think that through a bit.
Hans Gruber does it as misdirection, so that the feds will cut power to the building, and they can escape with the money and have the feds think they are dead afterwards. The ruse is to get people to do things they wouldn't if they knew your true goal, so that you can get to that true goal.
Thanos' false Malthusian logic makes people attack Thanos. He doesn't care, because he's personally the most powerful individual we've seen in the MCU to that point. Resistance is futile, an annoyance, and ultimately doesn't stop him, only barely delaying the inevitable. If the heroes can't stop him, why does he need a smokescreen?
And the movies' portrayal of him as this sort of "guy with a noble goal but bad methods" just seemed demented as a result. He didn't have a noble goal, he was a blithering idiot!
Agreed.
In addition, if we were talking about, say, Ronan the Accuser, whose real power base is religious and political, the false Malthusian logic would be a great reveal and allegory on the cynicism of modern politics and extremism.
But Thanos doesn't care if anyone believes in his cause. His power is based on fear, and his personal ability to squash you like a grape. He uses faceless stormtroopers, mindless ravening beasts, and a small cadre of thugs who seem to be in his employ because it gives them opportunities to hurt people. Who cares what Thanos believes? It isn't actually relevant to the plot.