Well, in political science and sociology, one of the most common definitions of the state is that it possesses a monopoly on legitimate/lawful violence.

Violence conducted via the military or police, according to regulation, is lawful.

But violence conducted by citizens, or by members of the government or military that is not according to law/regulation, is not lawful.

I'm not saying Twitter's drawing the line exactly right, but it's somewhere in the right vicinity.