The U.S. military took endless crap from the bleeding hearts over the Highway of Death in Gulf War One, when the objective--right or wrong--was exactly that: keep the military from coming back again.

As far as the current campaign was concerned, the resources required to capture and imprison tens of thousands of enemy soldiers* just weren't in the cards. Our troops were having a tough enough time just keeping supplies flowing for only themselves. The other alternative, a "highway of death" approach, pursuing and destroying fleeing soldiers, was judged inhumane, and not a good idea if you were going to occupy the place.

You need to remember that there was no way to distinguish, in many cases, professional pro-Saddam troops (the ones currently giving us a hard time) from poor conscripted slobs who would just as soon be home raising crops. There were a lot more of the latter than the former, I'd bet.

You also need to remember that the entire array of enemies currently ranked against us in Iraq is still only a very tiny proportion compared to the civilian population. And IMO a lot more of that civilian population is on our side because we did NOT annihilate them and their loved ones as they fled.

* This would maybe have been the ideal solution: pack them all away and sort them out one by one like we're doing in Guantanamo. In practice, this would have been hellishly difficult and expensive, and a political nightmare.