"everyone born here would have to leave. Then they would be replaced with immigrants."
Excellent plan. Here's my implementation:
Part the first:
All third-world population to move to USA, supervised by the UN. All, no exceptions. America becomes an exponential-GDP economists-utopia with a population of billions of ad-revenue generators. NY-LA greater metropolitan area. World GDP doubles. Trillion dollar bills on the sidewalk. Third world poverty ended. Sally Struthers retires.
Part the second:
The non-vibrant portion of USA is banished to the now-vacated lands. The ultimate liberal-revenge fantasy. Now they can experience first-hand the misery they inflicted on those people by not allowing them to immigrate here.
They can see first-hand life with the civil-wars, the gang-rapes, child-prostitution, drug-cartels, brutal dictatorships, AIDs. They will see what effect an accident of birth can have on your life. O Fortuna velut luna statu variabilis.
Then we will build a wall around USA so that they can never come back. They will try to climb the wall and beg for permission to immigrate, but their pleas will fall on deaf ears. See how it feels, hah. (Also, no one can leave either.)
The low population density will really make for a miserable GDP. It will be like living in a world-wide Australia, shudder.
I'm torn as to whether infrastructure left behind should be left intact or sabotaged. Immigrants are so industrious they won't need it.