Yeah, America will go far with that kind of attitude. 
Very far, as will anyone else who goes by this "attitude." Society does not and cannot operate on morals. It really is pointless to have any inherent "respect" for human life in that sense; humans are just another part of the universe, and we don't seem to have any "respect" for nonliving things.

(which is good)
Also, while it is indeed more rewarding to capture enemies alive, it is also much more difficult to do. Remember that after people heard the gunfire the whole place went up in pandemonium, and it would have become very easy for the guy to slip away in the confusion. Although in this situation, the whole thing seemed quite poorly planned (the guy should have started firing after getting on the plane, not at the airport terminal), and the operation did not have that bin Laden "master's touch" to it; the guy probably was not affiliated with any large terrorist organization, and even if he was, they probably only told him as much as he needed to know, so he would not yield much information. (one interesting thing is while Atta and one or two of the upper-level guys on the 9/11 planes knew that they were on a suicide mission, most of the hijackers thought that it was going to be a normal plane hijacking and did not expect to die)