We should never discard the Constitution, but adhering ourselves too closely to it in the wrong situations could end up shooting ourselves in the foot. One of reasons, among many many others, for why we're having such a difficult time in Iraq is that the insurgents know we have to stick to certain rules of engagement and simple legal/moral principles flatly stated out in our laws (which are freely viewable for anyone), and know exactly how they can abuse those rules and laws to cause us as much grief as possible while being completely uninhibited by anything resembling scruples of their own.
It's always better to be on the morally superior side, but if I absolutely had to pick between being morally superior and dead, or guilty that I violated my moral principles but alive and able to atone for such, it's going to be option number two for me. Along that lines, if endorsing a violation of this man's Constitutional rights means it could stop another Ft. Hood or similar attack, then I'll take that option and live with it. I take it for granted that other people don't feel this way, but it's how I look at situations like this with no 'good' answer, only 'bad' and 'less bad', with ambiguity as to which one is which.
And Paladin's got a point, the CIA probably already had this guy on a list to 'terminate with extreme prejudice', the only thing this does is bring it out of the black books and made public, whether such was politically motivated or not.