Really what this is all about is that we don't like that there are loopholes to begin with. Making judgement calls every time is a bad fix for the loopholes, and thus, the loopholes need ways to be written away; houserules.
my houserules don't ONLY cover some loopholes, they do other stuff, but the fact it, you can end up with a pretty large number of pages of houserules. I'm up to 14 pages, and that's not counting spells, classes, or feats, or abilities, just mechanics.
The use that would bother me isn't the prisoner idea, but if the players handle things right they can make alot of things a 'threat'.
Sneak up on a single town guard (who is armed and not considering the PCs an enemy) and then whack him for a bunch of hit points from behind. If they're lucky and time it right he goes down right after and he makes no noise cause they will have caught him by surprise.
Would the get away with it (maybe the first time). The issue is that, as a DM, I know I will have players who will try it expecting it to work, cause in the book, that IS how it works. I want them to know in advance what they can and cannot do, and don't want to make a bunch of wishywashy judgement calls.
Edit: Also, I should note, that doing this in a game would not necessarily get the player in
. I know DMs who reward this playstyle and consider it being creative. Hence me wanting solid rules that aren't easy to poke holes in (3.5 polymorph + Permanency anybody?).