The simple version: Weapons systems are quickly advancing to the point where many of them can navigate and operate independent of human control. The obvious question here is at which point do we give these platforms release authority for lethal weapons. It becomes impractical to require (or even imagine, really) there to be a human "pilot" operating every single drone when you have hundreds or thousands of them operating in theater. That's really what this is about.

Think of it this way: mines installed in the seabed in wars past were "dumb", in that a passing ship had to happen into it. Imagine systems deployed underwater that were mobile, contained multiple torpedoes, and could strike warships with little to no warning given their small acoustic signature. It's the same principal as a mine (you leave it one spot, hope an enemy ship comes by), but the capabilities are far more advanced. If the system is not at least semi-autonomous than it might as well be a dumb mine again.