The Iraqi capture of five Americans and killing of as many as 16 others is not any kind of victory for the anti-war movement or argument. It is a tragedy, but no hawk ever said the war would be without any casualties. What does make it regrettable is that putting American lives at risk in that way is not necessary to protect U.S. security.
But it’s no victory for the anti-war side for things to go badly. Unfortunately, I fear it’s a sign of things to come in Iraq under an American occupying government (still administered by Baath Party bureaucrats). There will be civil unrest, riots and war. The only question is how many Americans will die during that occupation and how long the occupation will last.