Build more cities. I don't understand the reticence in engaging in city building activity on a massive scale. That is what happened when America was explored,

Build more cities. I don't understand the reticence in engaging in city building activity on a massive scale. That is what happened when America was explored, wasn't it? More people == more scientists, engineers, lawyers, artists == more universities == more scientific breakthroughs. Eventually colonizing other worlds will become a possibility, and then humanity will expand there too, finally becoming free of Earth.