I agree that there should be no distinction between citizens and non-citizens. Targeted assassinations, no matter who they are of, are morally disgusting. Using drones to do the assassinations--which inevitably results in mistakes and "collateral damage" deaths of innocents--is even worse. We retroactively justify terrorists' behavior when we use the same methods (albeit with slightly different tools) against the people who happen to surround them.
Targeted assassinations are much less morally disgusting than sacrificing thousands of one's own soldiers and hundreds of thousands of foreigners - noncombatants and unwilling conscripts amongst them - in a declared war. The reason why political leaders generally argue assassination is less justifiable as foreign policy than conventional military intervention has nothing to do with morality and everything to do with them being more likely to be on the casualty list.
