I wanted to make a concrete proposal. Why does it have to be autonomous? Because in urban combat, the combatants will usually choose a firing position that has cover. They "pop up" from the cover, take a few shots, then position themselves behind cover again. An autonomous system could presumably accurately return fire much faster than human reflexes. (it wouldn't be instant, there's a delay for the servos of the automated gun to aim at the target, and delays related to signals - you have to wait for the sound to reach all the acoustic sensors in the drone swarm, then there's processing delays, then time for the projectiles from the return fire to reach the target)

Also, the autonomous mode would hopefully be chosen only as a last resort, with a human normally in the loop somewhere to authorize each decision to fire.

As for a threat to democracy? Defined how? You mean a system of governance where a large number of people, who are easily manipulated via media, on the average know fuck-all about a particular issue, are almost universally not using rational thought, and the votes give everyone a theoretically equal say regardless of knowledge or intelligence?

I don't think that democracy is something that should be used as an ideal nor a terminal value on this website. It has too many obvious faults.

As for humans needing to be employed : autonomous return fire drones are going to be very expensive to build and maintain. That "expense" means that the labor of thousands is needed somewhere in the process.

However, in the long run, obviously it's possibly to build factories to churn them out faster than replacing soldiers. Numerous examples of this happened during ww2, where even high technology items such as aircraft were easier to replace than the pilots to fly them.