I don't see the relevance of that point. The existence of violence without a particular weapon does not refute the argument that a new weapon may lead to even more death and suffering. By your logic since violence already exists apparently we shouldn't worry about new weapons making it even worse.

Back to the original point of the article it is important that international standards limiting such devastating weapons be enacted and enforced. Even Assad after being caught using chemical weapons was forced to step back and many robotic weapons, especially autonomous ones, should probably be in the same category for the same reason. These things are going to be developed so we need to act now to limit their use not wait until a calamity has struck.