Spoiler Thread: Avengers Infinity War

His comic motivations are lame. No plant life other than the Groot sentient beings were killed, as far as we know only sentient beings were killed off. Or else they would have made it a point to show animals and plants also being eliminated. The removal of half of the people consuming planets allows the planet and wildlife to recapture part of the planet, as shown in "I am Legend", meaning food will be in abundance. It doesn't matter if you get set back a couple generations of technological and social advancement, the resources most definitely increase.

In fact Thanos is pretty much Captain Planet.