I’m frankly astonished anyone could genuinely think the Avengers would ever somehow be more ok with letting Thanos kill “only the stupid people”. Like…that’s a very strange read on these characters to think they’d ever react any differently in this scenario.
But even if they were so morally and ethically bankrupt to think it may not be such a bad idea, the truth is killing “the dumber 50%” is still causing catastrophic secondary effects. People would lose loved ones. That’s enough of a reason to go Avenging.
Hell, how are we defining “dumb”? Because you may have just murdered every child under a certain age.