The US authorities have been literally gunning down black people for nothing for years.
Look, it's a dangerous precedent where a country can call someone a terrorist and take them out on foreign soil. The US entered Iraq illegally. They decided to force a regime change without lawful justification. It was those actions which have contributed significantly to the rise of Shia power plays from Iran and created ISIS, amongst other things. Meanwhile they continue to play happy families with regimes which fit the definition of "terrorist" which you seem to love so much and find so persuasive as a moral justification. So when you want to appeal to a moral justification in dealing with "terrorists", the moral force is somewhat questionable when, in fact, the real motive is political expediency.
This was a pointless assassination designed to give Trump fans a boner. I guess, on that basis, it worked.