Maybe one out of a hundred and you have to capture the right one. They compartmentalize information and its value declines rapidly over time. I say kill 'em and save every one alot of trouble down the road.
The fact that the compartmentalize information makes it all the more important to maximize the number of prisoners. The time value of information argues for the same goal. Intelligence gathering is putting together a hugely complex jigsaw puzzle, so why throw out so many pieces just for the heck of it?
Killing them all appeals to our emotions, so I sympathize, but it is logically counter-productive.