People can fly in 'easily' right now and just not fly out. We used to be able to walk across boarders with nothing needed or, at most, a drivers license and '2 billion people' didn't suddenly show up. This 'argument' that 2b people will suddenly come in has been tested and proven wrong. It is hard to move, especially when impoverished. It is hard to leave the things you know, even when you have a good plan and resources set up in the new country. Universally, the immigrants I have met are hard workers and make things better but sentiments like this one cheapen the struggles they have overcome to get here. The stats back this up with lower crime rates from immigrants and the economic boon they bring to the industries they dominate. It really isn't OK to spout '2b people will suddenly show up'. I flat out deny your premise and won't take your follow-up bait of 'can you survive if..'. We have survived and thrived with more open borders. It is only now that we are becoming weak and fearful because of tighter borders.