This reminds me of the movie Swordfish. Not that great a movie, but a good moral discussion. If it's ok to torture someone you think is guilty to save lives, how about killing them? They are a "bad guy" after all, what is their life worth to thousands of innocent people? And how about killing one or two innocent people? Sure, they aren't "bad", but how can you justify saving a few lives vs many more people who are equally as innocent? And if you are willing to do that, where do you stop? How about 100 innocent people, how about 1,000?
I know it's not the same thing, but once "saving innocent lives" starts justifying things you would otherwise think are wrong, really terrible things can be justified. One day you're torturing Achmed bin Talal who knows about a bomb at the Super Bowl, and the next your imprisoning Joe Smith for "thoughts agains the state". The problem is who do I trust to make those decisions on who's worth torturing? The fact is I don't trust anyone to make that kind of decision, do you?