Drones have several layers of added "decision making" that are out of human control making them far more dangerous. They get to autonomously decide, target, and kill based on many factors, using algorithms that we cannot trust or predict 100%. They also does it from afar. I know you can't trust a human 100% either but it's still the best we've got.
It's the difference between walking in a bog and encountering a lion. Both might kill you but they're in no way similar even in principle.
Autonomous killer drones are just automating murder and terrorism. Taking horrific weapons and making them worse by giving them better range, better targeting, and a brain that's smart enough to kill but stupid enough to do it as dangerously as possible.