Strawman. The only two alternatives are not assassination and letting someone go.
How about apprehending U.S. citizens who are suspected of terrorism and trying them in a military court? We'd need to change the law to create a definition for terrorists as being engaged in war activities, but that should have been done long ago.
Agreed on part one. I think we'd all be okay with shooting a guy with his finger on the button, so to speak.
As for the other part, I don't see why we need special tribunals. Makes far more sense from my perspective to try them in regular court.