If an American citizen can be legally and properly taken out by a sniper, as in a hostage standoff situation, then he can be legally and properly killed by a drone strike. The weapon used is immaterial. The legal issues are exactly the same.
Doesn’t it depend on who is issuing the hit? I don’t think that’s the same at all.
By the police maybe.
Non-combatants not engaged in combat are NOT targets of opportunity within our own borders.
All of America is not a war zone.