People are hacking on everything from micro-drones to full sized cars. Why single out this platform? Explosive on drones or automated weapons on cars could all be misused.
You really have no problem with a George Hotz purchasing a bot, soldering guns to it, installing some form of AI that controls the trigger, and then letting it loose into the world? Seems a bit irresponsible.
But to answer you questions about the legality all this - I don't know. Tesla and Uber are putting autopilots in their cars. Is that legal? Apparently, it is. Yet, those autopilots are already killing people. So expect a regulatory backlash, once enough people die.
I hope it won't take a massacre perpetrated by a buggy AI with a gun to get us there.