I quite simply don't view these men as soldiers.
If we were discussing Iraqi prisoners of war I would not advocate shooting them. However, these men are terrorists and also traitors - they are not soldiers.
Whether they were soldiers or not depends on the definition of 'is'.(A little Clinton joke, sorry.) If they wore uniforms, were part of a military type command group, etc., they were enemy combatants. If they didn't wear uniforms but did obey orders, then we could shoot them on sight, actually, without trial or paying attention to those pesky Geneva Conventions. 'It's complicated.' (Kerry, sorry.)