Didn't we (by which I mean the United States, the Soviet Union, and anybody else who got nuclear capability during or immediately following World War Two) have fully autonomous (for some definition of fully autonomous -- I'm counting dead man's switches) targeting and launching capabilities for ICBMs with nukes on the tips? Drones are at least discriminating; they aren't feasible to use for totally extinguishing a continent, even with the current US military budget.
Autonomy is interesting in the context of asymmetric warfare. Autonomy would finally fundamentally distinguish drones from very expensive remote control airplanes (in other words, our new-and-exciting weapon of the week is no longer something that an upper-middle-class american hobbyist would be able to throw together a passable equivalent for out of his own pocket in a few weeks), but mechanisms for autonomous targeting and navigation are information (and information derivable by a sufficiently intelligent group of people from experimentation, as opposed to the kind of information you have to buy, steal, or leak), which means that once a handful of details are known, the remainder can be deduced with an investment of time (as opposed to equipment). Autonomous drones would initially cost more than remote drones because of the research costs, but reverse engineering is cheaper than forward engineering, and (given that most of the prior work on these topics, so far as I am aware, is in the public domain in the form of academic and hobbyist papers) the capabilities of first-generation autonomous drones can be cheaply replicated -- and groups with little money and few cannonfodder units have much more to gain by arming and making autonomous a fleet of $200 toy airplanes than does the US military.