You Know So That We Can't Escape To A Better Country When The Shit Hits The Fan
So why would the government want to control who goes out sailing on a boat? For the same reason the government doesn't want us to fly out of the country without their permission. The United States Government doesn't want to repeat Hitlers mistake of letting Albert Einstein, Otto Frisch, Felix Bloch and Enrico Fermi* leave the 3rd Riech. It's not just to keep our enemies from building a new Manhattan Project to stop the Neocons from taking the worlds oil. The United States is the only nation that continues to tax its citizens income when such income is earned abroad. Work and live in another country for any amount of time and the US Treasury still expects you to pay your tribute to Caesar. Clearly we can't let any of the slaves decide to leave by airplane or boat when they realize the noose is tight and the whip is coming to get them.
Oh one more thing, that fence to keep the Mexicans out will do a nice job of keeping us in.
*Fermi was from Italy and not Jewish, his wife was, so he wasn't going to wait around Europe for something bad to happen to her.