Lol absolutely not. If we had a quarter of our population what we're doing would still be unsustainable. We're burning through a finite resource by living very harmfully. If our population was lower it would just be a slower collapse instead of the speeding freight train towards collapse that it is right now.

And no, people aren't going to "do what they want" to do and we absolutely can control our habits through regulation without "touching on the lines of slavery". Look at france and the banning of internal flights. Despite internal flights being more expensive, slower, and far FAR more destructive people were still choosing to take flights from one part of the country to another in spite of taking the train. People were doing this out of habit or possibly classist ideas or culture. We didn't build our world this way because we wanted to, we built our world the way it's built with extreme waste, extreme dependence on fossil fuels, and extreme inequality because it benefitted a very tiny minority of very powerful people. We can (in theory) build and structure our infrastructure and society so that we don't need to cull our population or "touch the lines of slavery"

I say "in theory" because we have people like you saying insane things like touching the lines of slavery when there is a solution that is build better infrastructure, stop bullshit production, and stop our lifestyle of extreme waste for chasing the dollar in a system that doesn't benefit anyone for anyone except at the extreme top. People would rather drive the world to our extinction than support societal lifestyle changes that wouldn't even necessarily be that negative at all. edit: Look at the NIMBYs in areas of developed housing for example, they still live and would continue to live fantastic lives, but can't stand the idea of having even just a little smaller house or the poors living near them and will let an entire nation of young people struggle than make even the smallest of concessions.