One of the things that we are supposed to do with our faculty for reason and adaptation is to confront each new issue and challenge with solutions that work within the framework of American ideals - not lock ourselves into a death pact that confines us to reactive moves only.
In other words, hanging a terrorist after the fact brings scant comfort to his victims and does not dissuade his colleagues one iota - shutting him down in advance works one helluva lot better.