That's the catch, though. What if you wanted to move? That would have sucked. What if you had to move? That could have been disastrous to you. What if you had lost your job, and defaulted on the loan. Apparently most states in the US are non-recourse, so how would you feel when your next job's wages are garnished, or there's a lien on the next home you buy?

When you have to put an "If" in front of "being underwater doesn't mean anything", then that means sometimes it really does mean something.