You know, after a day I'm still struck by the sheer stupidity of MCU Thanos's villain motive which just doesn't make sense any way you look at it.
First and most importantly, populations aren't static and will inevitably regrow until whatever problems they might have faced will once again become an issue, yet Thanos thought his work would be done after a single snap. However, you'd really need a recurring method of culling. (Which was a major plot point in... well, I guess I can't say the anime's name up here without spoiling that.) As a forward-thinking individual, Thanos should clearly be intelligent enough to recognize this issue.
Second, the needs for a population will vary drastically planet by planet. While choosing half a population might work to cover a potential overage even if the planet can support five to ten times its current population, it's not going to be nearly enough in other cases to substantially move the needle. That said, it's nowhere near as bad as #1 because it could reflect a pragmatic decision.
And finally there's the very simple matter that instead of culling the population to address resource limitation, he could have simply used the Gauntlet in a different way to address those issues without killing anybody. He could have created new resources, a means of continually creating/recycling resources, changed peoples' physiology (so they could survive while consuming fewer resources, different resources, or no resources at all), etc. And honestly, what's the point of having a god-like device if you're going to do the exact same thing you've been doing but on a larger scale? And even when he was talking about recreating existence, it didn't sound like he was going to address *any* of these issues.
I realize that I've probably put more thought into Thanos's motives than the films' creators did. As it is, the motives are more nonsensical than just having Thanos do it so that Death-sempai would notice him.
As for the anime spoiler: I'm talking about Gurren Lagann. (Major spoilers) The population in the anime is driven underground by a race of beast men who prevent humanity from re-establishing themselves, building cities, and growing in size. It's revealed that the beast men are doing this at the behest of "Lord Genome" to specifically limit humanity's size, keeping it under a certain amount... because in the distant past Lord Genome lost a disastrous war against another race of super-evolved beings who iirc made it clear that if humanity was allowed to grow beyond a certain point, they'd return and attempt to wipe out humanity. As such, LG represented the lesser of two evils. And this other race -- the Anti-Spirals -- were concerned that Spiral races like humanity would grow and evolve to the point where, among other things, they'd pose a serious threat to the Anti-Spirals. Of course, there's a lot of weird shit in the anime that keeps it from being a grounded scifi.
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(\/)(\/)|-| There are precious few at ease / With moral ambiguities / So we act as though they don't exist.