The military tribunals currently underway at Guantanamo Bay create a clear legal process, as affirmed by the U.S. Supreme Court in Hamdi v. Rumsfeld, for adjudicating the cases of these terrorists, when possible. Those efforts would be severely undercut by moving the detainees to the United States.
Americans different in some maybe thoughts or emphasis still have the same ideas. They want a government that lets them be free, that leaves them alone, that doesn't interrupt and interfere with every aspect of their life, that lets them go to work and keep more of what they've worked hard to have.