I've been keeping track of this debate ever since it made the big splash a couple years ago.
The best explanation I've heard so far is the one liner that the president and several republican reps and senators have been saying for a long time now: "We are doing what is necessary to insure the safety of the American people."
Just last night, there was a debate about a similar issue. The democrats were saying how America has been known as the nuremberg nation for the last 50 years and the last thing we need is for the world to start thinking that we are now the quantanamo (sp?) nation. Immediately, a republican rep responded by saying that the democrats aren't willing to take the necessary steps to keep this nation safe. It's more complicated than that and you may be hearing from a very bias perspective (mine), so sucks for you for not keeping track of the politics.
But the point is there really has not been any good explanation for the act.