Thanos, a philosophy and economics double major who thinks once you eat a plant it will never grow back: i have to slaughter half the universe's population with the infinity stones, so that no one ever runs out of resources and starves
Thor, a phys ed and linguistics major with a minor in women's studies, taking a sip of his strawberry protein shake: can't you just use the infinity stones to create more resources tho?
Previously, previously, previously, previously, previously, previously.
I don't get all the people who say "well, why wouldn't he just create more resources instead?"
He could, but that's just not how he's thinking. He didn't start from the premise "I should get all the infinity stones." and conclude "Hey, I wonder if I can use the infinity stones to solve this problem of too many resources and not enough people, and if so what' the best way of using them to do that."
Rather, he's starting from the premise of "I need to solve the problem of too many people and not enough resources, and the only way I've been able to do that for at least decade (see young Gamora flashback) has been travelling to planets one by one and rounding all the people up and slaughtering half them, and that's exhausting - what's an easier way to slaughter half the people on all the planets in the universe?" and concluding "I should get the infinity stones."
It's like the opposite of Maslow's Hammer; if every problem you've ever had is a nail, any tool can be pressed into service as a hammer.
He also could have used the stones to adjust the fertility rates of every race in the universe so that they naturally fall to sustainable levels over the next few thousand years.
Who do you think he is, Jimmy Carter? "But I don't want to cure cancer, I want to turn people into dinosaurs!"
Achieve ultimate power; replan party; roll a beta; sleep it off; make a titer plate of reborn civilizations and their biota that roll a little smaller or more progressive; keep logs; plan party; do the weird thing; see it turn out successfully based on previous not failing to swole; conceptualize a reward.