If you drew a Venn diagram where the people in circle A want to cull the human population and the people circle B want to disarm the human population you would find that most of circle A falls within circle B. Whenever somebody suggests human population control I purchase more ammunition.
The control of the human population has always been around, why do you think so many countries are so ready to jump to wars? It's the price of the economic system we have nowadays, not that it would be different with any other economic system... But basically, according to the malthus theorem, population will continue to have a more rapid growth than resources, and the only way to make sure not everybody dies is making sure the population count "restarts" now and then, with wars and diseases... I'm not saying this is some kind of all powerful conspiracy among all countries but rich people make a lot of decisions based on how to stay rich
Why is everyone's first assumption that this means culling or eugenics? Birth rates in wealthier nations have been dropping naturally for a while. It used to be common for everyone to have 5 or 6 kids or more, now it's down to an average of 2 or 3. Access to birth control in poorer areas, better education chances for women in developing nations, and access to better healthcare and nutrition have all been shown to both improve people's lives and allow them to keep their families smaller. Give people control of their lives and they're often content with smaller families. This is good for the planet AND the people.
The environment isn't in any danger. The worst we could do is make the environment too hostile for us to survive, so the problem would just solve itself.
Start and finish with yourself.