Could you break down the logic that leads you to this conclusion?
Im sure it's deeper than "if cities disappeared right now, a lot of people would disappear with them"
I'm sure all of this was inevitable as there likely hasn't ever been a time where humans were not getting together to form communities when it was beneficial to do so.
You don't need to. Fertility rate per woman in wealthy countries decreases every year.
Growth is natural, overconsumption is not.
Oh give me a break. Developed countries have had below-replacement fertility rates for decades.
If your goal is to reduce birth rates, we do the things that we already know do that naturally: comprehensive, fact-based sex ed; cheap and easy access to contraceptives; social safety nets and support; etc etc etc.
It's not a mystery and it's not even difficult. You don't need to jump to straight to abhorrent crimes against humanity.