Aside from the fact that drone striking would be like cops throwing grenade which could cause massive colateral damage, you jump into the issue of responsability. A cops who fuck up is a person. the system is far from perfect, but you know who fucked up. A drone strike is a chaine of command fully disconnected from reality where it take place. It means that you'll have specific code to follow and if anything break the code, then you'll have approval. And if someone fuck up, the code will be sued and modified instead of someone. Which doesn't seem like a good long term resolution.