Earlier quoted context omitted.
Because congress is afraid that they will break out of prison and kill people. The ones that are getting released probably don't want to come to the States anyway on account of lynch mobs. On a side note, I was clearly mistaken and this includes the one we tried to get Slovenia to take. After the full-body scanners and COICA I'm getting a little on edge about my support of Obama.
How many lynchings have occurred in the US in the past 30 years?
I have no doubt that anyone released from Guantanamo into the United States would be subject to harassment, if not actual danger. The people in congress arguing vociferously against their release must have reasons, and as far as I can see that's either the belief that everyone in Guantanamo deserves to be there, or the belief that it will result in violence if they come to the US.
And simply put, in this case the expectation of violence is as good as violence itself. That's the goal of terrorism, and it's worked extremely well.