The problem is we know now many of the people at Guantanamo do not fit that description. And we don't know how many do and how many don't, because there is no legal process to make the determination.
After WWII, at least there was some kind of war crimes tribunal before executing people for war crimes. But Guantanamo is some kind of horrific, Kafka-esque limbo, where people can be sent for being in the wrong place at the wrong time or accused by someone just wanting to collect a bounty, where people can be held forever and tortured on a whim, with no prospect for any kind of closure, ever.