I agree that "making laws" isn't necessarily a solution, but it lays the foundation of future debates. This topic would no doubt involve a ton of debate and it would be VERY useful if it materializes into international law. "Why" you ask?

Well because when someone violates it, there would be no question of whether this is right or wrong. We wouldn't have to go through the whole above debate all over again, just to come to a consensus that this was evil. You could just cite the law and (hopefully/in an ideal world) prosecute.

Ps: They still might be able to cirumvent drone strikes by saying that by defintion of war agreed upon in the first geneva convention, it isn't war. so this rule doesn't apply. I hope they think of this when making the law