If we resort to the same measures terrorists resort to, what makes us any better than them? You say we are doing it for the better good, but who decides what is the better good? For us, it is protecting our lives. But they think they are doing things for good too..."protecting" their religion (or misguided views of it) and their people, or ideals. Obviously we think they're wrong, but my point is that we are both fighting for what we believe is right.
So what separates us from terrorists? It is how we go about it. Terrorists rule with fear. They instill fear in people's hearts so they fall, and give in to the terrorists' wishes. If we rule with fear as well, what makes us any better? I understand that we need to take harsh action against harsh people. But at what cost? Is it worth it to lose everything our country stands for? Our country is run under the principles that every man is equal, and has equal opportunity under our law. Unfortunately, that applies to the scum of the earth as well. A fair trial does not mean we let them off. A fair trial just means that we are upholding the principles of our country. And if we say "screw our ideals" then that puts us at the same position as the terrorists. If we reject our country's promise to be just and fair, then how are we any better? We are also ruling with fear, unfairly using force to gain power. And if you can so easily throw away such a fundamental right, oath, in our government, that we swear to give everyone fair trial, then what is stopping our government from throwing away other rights as well? In a civilized society, we can't always take the law into our own hands. yes, sometimes rules are wrong, but if a rule is changed, it should be changed for everyone. If we want, as a society, to give equal treatment to everyone, we can't decide who "everyone" is. It is all or none, and that is a sacrifice we have to make in order to keep from falling to the same level as the terrorists.
Sorry, I was rambling. maybe I made sense, maybe not, but my point is that it is not because we feel bad for the terrorists, or think talking to them will help, it is that Guantanamo is a symbol of the same fear terrorists use, and fighting terrorism with terrorism is only going to put us at their level.