That would be the decent thing to do, but Congress has explicitly blocked that. Under no circumstances can a detainee be transported to the United States.

Right, but the President and Congress are not elected to do the "decent thing" but rather to implement the will of the people. When the Senate voted to block transfers from Guantanamo to the U.S. by 98-0, that suggests that they understood that the political will in the U.S. was strongly against such an action.

I apologize - I didn't know that had explicitly been blocked.

Exactly right! To our shame, the reason decent things don't happen isn't because they're impossible, but because they might have some political fallout. To a certain species of troglodyte, "impossible" and "some political fallout" are the same thing.