A Texas company, Chaotic Moon, has come up with a self-piloting drone that can deliver taser attacks. It's aptly named Cupid. Future versions of this technology, which the company is said to already be working on, will pack pepper spray and EMP guns. I can imagine all kinds of other onboard weapons on these things: lasers, gatling guns, poison darts, tear gas, etc. http://youtu.be/MzKvTPmv8z4
I think a lot of small drones are going to get shot down, especially the weaponized ones. Folks targeted by stunner drones aren't exactly going to welcome them with open arms. Drones will need ways to protect themselves, otherwise people are just going to take them out, wholesale. So I think they'll eventually have self-defense capabilities, either built-in or in the form of separate robots (or humans) that provide backup. No idea what that will look like ... maybe onboard motion detectors along with facial recognition and a predictive algorithm that senses when someone is pointing a weapon at the drone, and pre-emptively zaps them.