Bodhi, for the actual fighters, sure, that makes sense. But _some_ of the people being detained have been found innocent, and there could be more. We were paying Pakistanis and Afghans for people they delivered that they said were terrorists, and that word was the only evidence.
You're not advocating that the innocents should also be killed, are you? Because that'd be the most likely side effect to a "just shoot them all" policy.