It isn't rocket science to understand the concept of scale. One person in a hundred is worth more than one person in a million. The argument behind population control really should be more towards forcing companies to generate better infrastructure across the country instead of focusing on a handful of gigantic concrete strongholds. Giving people the ability and reason to move out of the city will solve overpopulation problems within cities. Though I'm not certain that we can spread this many people across our country in a safe or meaningful fashion.
This isn't about just "how many people can survive in the landmass of the USA", it is about overpopulation at hot spots. 9 million people in the state of New York is one thing, 9 million people in the CITY of New York is quite another. Studies have actually shown a distinct correlation between higher population density and higher rates of depression, stress, drug addiction, respiratory disease, cancer, and even short-sightedness developing due to view blocking buildings. People didn't evolve to live inside these cramped spaces and sitting in cubicles all day.
https://www.newgeography.com/content...ss-and-density
[edit] I will concede that suicide rates tend to be higher in rural areas, though I assume that is more due to social stigma. It is easier to go kill yourself in a field alone, than it is to hang yourself off the edge of your third story apartment for all to see. As funny as it sounds, it's very possible that people don't kill themselves because it would be embarrassing.