The doves claim that the Afghanistan war and especially the Iraq war are counterproductive. The concept is that these wars have greatly increased Arab humiliation and anger, and as a result, for every terrorist we've killed or captured, ten more take his place.
The hawks claim just the opposite. Arabs may be angered, they say, but the Islamic extremists attacked us because they thought we were weak and decadent. Like anyone else, Arabs prefer to bet on the "strong horse" so it's imperative that we show we're stronger than the terrorists.
Unfortunately, this is the wrong debate. It doesn't really matter how many terrorists there are. It only matters how effective they are cumulatively. For example, if our foreign policy causes ten times as many terrorists, but each terrorist is only a hundredth as effective, then that foreign policy is a resounding success. On the other hand, if our approach gets rid of all the terrorists but one, but that terrorist has a nuke and sets it off in New York or some other densely populated area, then that approach was a total disaster.
So, don't worry about how many terrorists there are. Think instead about the total damage that can be inflicted by the set of all terrorists as a result of our foreign policy. It's a much harder analysis, but at least it's a more useful question.