No, America is not full. Not by any standard any reasonable person might want to fly. Now if we were the UK with a population density approaching 800 people per square mile maybe. However, we’re still shy of 100 people per square mile with enough natural resources to employ ten times our number.
Does your density number include the thousands of square miles of the uninhabitable West?
Clearly you have not looked at how our population is distributed.
Those wonderful “Cities” are the toilets of our culture, we do not need more crowding, or foreign languages and cultures to divide us.
We do not need more imported disease carriers, spies, etc.
No need to repeat my entire earlier post, you enjoy all that wonderful “Diversity”, in all it’s forms, I will work on getting our borders closed.