We have more than enough resources for more than the world's population. The problem isn't overpopulation, it's manufactured scarcity. Telling people to just have less kids is victim blaming when capitalism requires letting some people starve to maintain the artificial value of products.
the resources aren't the problem (although i would still only half agree with you on that statement). it's the quality of life. do you want to live your life packed into an apartment? do you want to get on a 5 lane freeway to go get groceries? do you want to go to a state park and not be able to find a parking space? do you like crowded spaces? do you want to continue to burn rain forest to create range lands? do you want to watch the suburbs continue to expand into natural areas? do you want to continue to global warming?
we are a much more sustainable species at half our current population level.
You're proposing population culling, which is a classist and racist proposal. I'm not sure how exactly you propose to implement that, castrating poor people, who usually have more children? We want a world for future generations to enjoy.
My usual counter to your "solution" is: mass suicide is even more effective than not having babies.