There was a German terrorist trying to shoot up a Synagogue in Halle. He had an impressive stash of homemade firearms yet none of them were powerful enough to actually open the thick wooden gate to the synagogue. A ladder and a knife would have killed more people.

You're going to run into the same situation with drones. It is easy to imagine some super complicated drone based attack scheme when there are far simpler and more effective methods of taking care of a target involving firearms.