The biggest problem with this is that this is perfect for political assasinations. It can be precise enough and it can be probably leave little traces or be made hard to identify who was controlling the weapon - just like now we have problem with identifying the sources of internet attacks.
I remember reading, many years ago, a very short SF story about a robot built specificially to kill targeted people and leave false traces. I think even now it would not be too difficult to built a small bug-like (or wasp-like) robot with a poisonous sting that could autonomously navigate a few hundred meters to reach a bed of a politician (or activist) - how are you going to protect your leaders against an attack like this?
You'd have the same problem identifying the source of a sniper's bullet, in the context of a world where the government is willing to take people out like this.
Looks like it was not that easy - even for a superpower like the USA. Now imagine that they had miniature bots that could follow the target (and then kill him).
I remember reading, many years ago, a very short SF story about a robot built specificially to kill targeted people and leave false traces. I think even now it would not be too difficult to built a small bug-like (or wasp-like) robot with a poisonous sting that could autonomously navigate a few hundred meters to reach a bed of a politician (or activist) - how are you going to protect your leaders against an attack like this?