When you have a group of prisoners that you are getting info. from you can use the other prisoners to find out what is true and what is not. A skilled interrogator can tell from body language. For instance under water boarding the guy tells you they plan to blowup a blue building and when he tell another that we know they plan to blow up a blue building that person will show some sign that will say if we are on the right track.
We hold our self to a higher standard to our determent.
I could have some serious fun with the logical extreme of your last sentence.
Perhaps we should do like the Russians did? Some Islamic extremists at one point had captured some Russians (not sure who; I believe they were government officials). The Russians' response was to find the extremists' families, chop a finger off of each one, and send it to the extremists. It worked. Should we do that, too, since it "works?" Perhaps we should also capture relatives of known and suspected terrorists and threaten to torture them to death?
Trust me, the ends do not justify the means. What, precisely, is the purpose of going to war if we're going be just as evil as the enemy? The fact is, some things are wrong, plain and simple. Indiscriminate killing of civilians is wrong; torture is wrong; using innocents, directly or indirectly, as human shields is wrong; killing soldiers who have surrendered is wrong; and so on and so forth. We're supposed to be better than that. Aren't those types of things what terrorists do? Then again, government today, almost without fail, is just one big terrorist organization, so...