Once again, drones can level an area or kill fighters, but you cannot secure an area effectively with them. You aren't gonna replace boots on the ground with a couple of quadcopters or even the land drones Ukraine has been using, and despite the Secretary of Defense apparently not knowing that, the people that actually make decisions should. Unless you're talking something like a stand-off violence parade where a protest happens and then 20 minutes later a drone strike happens in that spot, I simply do not see a replacement for having equipment and men on the ground.