If Thanos had, instead of randomly wiping out 50% of all living things, he had instead in each species wiped out only the dumbest 50% what would the reaction of each avenger have been?
Why on Earth would the Avengers react any differently? Is the assumption that they're morally bankrupt enough to actually reconsider in this scenario? That somehow letting "stupid" people be murdered is ever, in any way, acceptable?