I would see DDOS as a violent attack. Violence is never justified. When a person afflicts another person's computer with a virus, or even a bot attack, then an act of violence is being performed--not on the computer, but on the person. When citizens of one nation attempt a DDOS in a concerted effort against another nation's infrastructure--like power grids, communication channels, etc.--then that is an act of violence akin to declaring war. As a DDOS becomes easier and easier to do, then the likelihood of it happening and inflicting serious damage becomes more and more likely.