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?
Thanos was a fucking stupid character in the MCU. The human population is currently doubling every 61 years with a growth rate of about 1.14%. Assuming similar numbers across the galaxy, he didn't do anything except cause suffering. He's a very poorly written villain.
I guess to stay on topic, they would have looked at population growth, and determined that his plan was moronic, and fought him.