TENS OF THOUSANDS OF PAKISTANIS are still marching and rallying to express their anger about the U.S. airstrikes on Friday that were meant to kill Ayman al-Zawahiri, and instead killed between 17 and 30 civilians, including at least half a dozen children.

To fire four Hellfire missiles into the heart of a residential neighborhood, CIA officers must have had reason to be convinced, and even certain, that al-Zawahiri was in one of those houses. Because they wouldn't have taken the risk of killing so many innocent people unless they had rock-solid evidence that Zawahiri was there, right? Here is the intelligence that was so superb and so compelling that it left no doubt Zawahiri would be there:

Pakistani intelligence officials said the reported target, al-Qaida No. 2 leader Ayman al-Zawahri, had been invited to the attacked village for a dinner marking a Muslim festival on the night of the missile strike but he failed to show up.

He had been invited to dinner! And of course there was no question that he would show up. It was a certainty. So on the basis of a dinner invitation, the U.S. bombed an entire village, and now Zawahiri is still alive, while 18 or more wholly innocent civilians are dead.

We are constantly being told by war supporters that airstrikes like these are necessary to pick off Al Qaeda leaders. But that view is terribly myopic. Take a look at what's happened here. By killing scores of civilians and completely missing Zawahiri -- because he wasn't even there -- the U.S. has made our position much, much worse with not even one positive thing to show for it. If Zawahiri had been there, and those airstrikes had killed him, America's national security would not have been increased by anywhere near as much as our security has been damaged by the deaths of those 18 civilians.

Barbara O'Brien makes this point quite well:

Even if the raid had taken out Ayman Zawahiri, one might still argue that the price of the capture was far too high. "This is war, and unfortunately war results in collateral deaths by mistaken targeting," say the warbloggers. But let's take a step back and ask a fundamental question.

Why are we at war? Aren't we supposed to be fighting to end (or, at least, significantly discourage) terrorism? If our focus on eliminating people on a shopping list of bad guys results in making more bad guys, is this not a tad self-defeating? Like curing someone's headache by cutting off his head? Are we not missing the big picture here?

It's a simple cost/benefit calculation. The benefit to our national security gained from killing one Al Qaeda leader, or attempting to kill him and failing, is far less significant than the cost to our national security of killing innocent women and children in that attempt.