Well, I think one of our chief goals is to get Afghanistan and Iraq to stand on their own, anyhow. At that point what they do with the terrorists they catch will be their own internal affair.
But terrorists are all over the world, NOT just in Afghanistan and Iraq.
They just arrested some in France with ties to Zarqawi.
What if we capture some terrorists, who planted a nuke somewhere in the US, which is on a timer to go off, but we can't use even "degrading" techniques, never mind cruel ones, against them to find out where the bomb is, because the interrogation officer will get prosecuted by US law?
Oops, there goes New York, or Washington DC, or Boston or LA or...
Even if they release them or cut a deal with them that the west don't like?