Earth is not overpopulated. The problem is that certain places have too much population density. If everyone spread out across the world there wouldn't be any of these issues. For a variety of reason people can't or won't spread out.
A single apartment building uses far fewer resources per person than the equivalent number of people would if they all had 10 acre lots in the countryside. The habitat destruction alone would be an ecological disaster.
Beg to differ. Exhibit A: climate change. Your solution would not ameliorate climate change. In fact it would likely exacerbate it. We need as much of the land as possible to be rewilded(left alone to maximize CO2 absorption and heal the planet). And stop having babies. Do you really want to bring a child into the nightmare we are barreling towards?