With all due respect, my friend, this is the weakest argument I've heard in awhile. Americans don't plot terrorist attacks on other countries -- our society is healthier than that. And if Americans were plotting terrorist attacks, we'd find those people and lock them up ourselves.
If the Gitmo prisoners go back to their home countries, they'll be released soon to plot new 9/11 attacks on us. That's okay with Jimmy Carter, but it's not okay with most of us.
So give them trials and execute them. I have no problem with that. But just holding them down there seems stupid to me. What's the point? If we think they've actually done something, give them a trial and convict them. Personally I think most of them are just Joe Mohammeds who were picked up "fighting for their country". Just as Joe Americans would be here. Doesn't make them terrorists.