Because if we're caught breaking the law, the terrorists win.

And the damage to the presidency continues... This time the minions of President Doofus are arguing that they shouldn't have to reveal details of how a Belgian bank provided the US info on various banking transactions, possibly (probably) in violation of the law. Why shouldn't they release information on whether or not they broke the law? Because...wait for it... it's a state secret.

The problem, of course, is that this looks awfully convenient, that the motivation is more of the regime's Administration's desire for secrecy for its own sake. So it's going to be that much harder for the next President to make any such argument. For that matter, it's going to be harder for the regime Administration to keep making that point if they keep overusing the "it's secret because we say it is, and you don't need to know why" defense:

Historically, courts have been reluctant to challenge the secrecy privilege. But the administration has suffered setbacks in seeking to use the secrecy claim in the eavesdropping case and several other recent cases.

“We’ve seen a real erosion of the ‘state secrets’ privilege in the last year,” said Mr. Schwarz, the lawyer suing Swift. “I think it is from overuse. We’ve seen it used in record numbers, in situations where it was inappropriate, and the courts are starting to recognize that.”