The purpose of Guantanamo was to hold prisoners who were difficult to try conventionally. If we give the government the benefit of the doubt (and I'm willing to, though I'm sure many are not), the remaining Guantanamo prisoners are those who were probably guilty of something and would likely have committed violence if released.
At least some who have been released have, in fact, returned to fighting:
So if there's any good that came of it, then it's in the counterfactual: the violence that wasn't committed by people detained there.
Now, that's asking you to believe the US government, which I don't think is unreasonable -- though it's also reasonable to hold serious doubts. And even if you're willing to grant that benefit of the doubt, there's a very strong case that whatever counterfactual harm has been presented has been more than outweighed by the harm to US standing in the world -- including its own people. As well as the simple harm done to actual human beings who are there, without jurisdiction to challenge it.
Nonetheless, I think it's a decent answer to say that it's "good" if violent terrorists were prevented from harming people, even if you can't actually prove that they would have done so. If you're going to judge the merits of the thing -- and I wouldn't disagree for judging it very, very negatively -- it's worth acknowledging that much.
Guantanamo has kept some people (outside the US) aware that if they believe themselves to be on the right side of a conflict and they want to be seen by others as being right, then they'd best not do anything like Guantanamo. That no matter how popular you are now, doing anything like that will lead you to lose popularity karma.
The purpose of Guantanamo was to hold prisoners who were difficult to try conventionally. If we give the government the benefit of the doubt (and I'm willing to, though I'm sure many are not), the remaining Guantanamo prisoners are those who were probably guilty of something and would likely have committed violence if released.
At least some who have been released have, in fact, returned to fighting:
https://www.dni.gov/index.php/newsroom/reports-publications/...
So if there's any good that came of it, then it's in the counterfactual: the violence that wasn't committed by people detained there.
Now, that's asking you to believe the US government, which I don't think is unreasonable -- though it's also reasonable to hold serious doubts. And even if you're willing to grant that benefit of the doubt, there's a very strong case that whatever counterfactual harm has been presented has been more than outweighed by the harm to US standing in the world -- including its own people. As well as the simple harm done to actual human beings who are there, without jurisdiction to challenge it.
Nonetheless, I think it's a decent answer to say that it's "good" if violent terrorists were prevented from harming people, even if you can't actually prove that they would have done so. If you're going to judge the merits of the thing -- and I wouldn't disagree for judging it very, very negatively -- it's worth acknowledging that much.