If we kept the ones "we have reason to keep" - which would probably mean all 500 or so current detainees - but closed Gitmo, we could bring them to the United States. But this would be a legal quagmire, as it isn't clear what their rights would be on U.S. soil. And it would be a disaster to treat them like common criminals with all of the usual constitutional rights. Nobody read these murderers their rights when they were seized in Afghanistan, and it's not like the cast of "CSI: Kabul" or "Kandahar PD Blue" collected all the necessary forensic evidence to build a case against them. Does that mean we should just let them go? We certainly can't set them free on American soil. And if we send them back to Afghanistan or Pakistan, it would be like giving them a do-over.
Any new Gitmo would quickly gain the same reputation as the old one because a) al-Qaida is under strict orders to allege all manner of abuses for propaganda purposes, especially now that such tactics have proved so useful, and b) because the "international community" and other lovers of runny cheese desperately want such allegations to be true, regardless of the evidence. That the head of Amnesty International could call Gitmo, where we spend more money on the care and feeding of detainees than we do on our own troops, the "Gulag of our time" is all the evidence we need for that. Caving into such bullying would send the unmistakable message that American can be rolled.
Now, none of this is to say that the U.S. military should have carte blanche to torture or harass detainees. There must be rules, and it is perfectly fair to debate what those rules should be. But unlike the lawless calamity of Abu Ghraib, the evidence is sparse that Guantanamo is anything like the house of horrors depicted by its detractors. In other words, if there are abuses, remedy them. If allegations are propagandistic lies, rebut them as best you can.
But caving into a defamation campaign in order to please those who cannot be pleased and aiding those who must not be aided is no way to support the war on terror or prevent more victims like Louis Pepe.