'War' is a very specific term of the trade. Using any and all tools available when you are at War can be easily defended by a whole lot of people (not everyone0. US is not officially at war in Yemen or Pakistan or for that matter Afghanistan. Hence, I think, use of drones introduces another dimension to the arguments. Ultimately, there is and always has been one principle used by humanity - 'Might is right'. Of-course smart ones can always hide this core principle in layers of arguments of convenience.