The problem is not with the borrowing; the problem is that Social Security's asset base consists of the government's ability to borrow money. It is usually a really bad sign when someone says "I totally can't pay off this loan, but I know this guy who is willing to lend me more money because he has no idea how financially irresponsible I am."
No, the problem is with the borrowing. When our nation borrows that much, everyone's asset base consists of the government's further ability to get money (by borrowing, printing, etc.). That's the way free floating currency works. Having to print $4 trillion to put the money back in Social Security is the same to every American as having to print $4 trillion to give to China.
