Like, where does this come from? Even people that aren't particularly conservative seem to think that less people = good. Maybe the problem isn't the amount of people but how their needs are met? Yes, the world is finite, but pretending that hunger, homelessness, wars and diseases are in anyway caused by the amount of people on Earth rather than how we deal with those things is as insane as denying climate change.
I can say, personally and perhaps anecdotally, that a lot of the problems I experience are in contexts where I feel crowded and in competition with other people. At least in Amerikkka most people spend a significant part of their lives trapped in an enormous steel line surrounded by too many cars unable to go anywhere, waiting in lines for limited quantities of necessary goods, and fighting to have space to yourself in the decreasing number of public spaces available without having to pay to enter.
I know better than to blame the people around me for these conditions, but I think a lot of people tie those frustrated feelings to the people around them instead of to the systems that create the jams.
I'm not saying this fully accounts for it, but I think people get a strong vibe that things would go smoother without all these people around.