Imagine a mine that could move around, target seek, refuel, rearm, and kill hundreds of people without human intervention. Comparing an autonomous murder machine to a mine is like comparing a flint lock pistol to the fucking gattling cannon in an a10.

For what it's worth, there's footage on youtube of drone swarm demonstrations that were posted 6 years ago. Considering that the military doesn't typically release footage of the cutting edge of its tech to the public, so this demonstration was likely for a product that was already going obsolete; and that the 6 years that have passed since have made lightning fast developments in things like facial recognition... at this point I'd be surprised if we weren't already at the very least field testing the murder machines you described.