The "extreme" left, the sort of people that attack folks that attend milo events, have clearly communicated that they believe violence is a legitimate response to a difference of opinion. They have also clearly communicated that they don't believe that property rights should be respected in such situations as they break windows, damage businesses and generally vandalize buildings.
However, even less "extreme" members of the left have demonstrated that they don't respect these things either. That is to say, the folks on the left who physically attack attendees of conservative speaking events are simply taking the leftist ideology to its logical extreme.
If you're on the left, you genuinely believe that taking money from successful people in order to help people you perceive as needing it is a "good" thing. That is to say, as a leftist, you believe that people you don't know with less money than you think they should have should be given money taken from "rich" people. Whether the rich people agree or not.
If you're on the left, you believe the "greater good" is achieved by taking money by force if required, from people who have more to give to people who have less.
How can that be? If a man holds a gun to your head and demand you cook soup and hand it out to the poor, does that make you a good person?
How is this any different to what the government does? Taxes are taken from "rich" people and given to "poor" people in the form of direct welfare, public schooling, subsidized child care, public parks etc... If you don't pay taxes, you're threatened with imprisonment. If you resisted imprisonment, you'd be violently restrained. If you tried to defend yourself you'd be shot.
That is, the demands of government are really just veiled threats. They're demands backed by threats of violence.
Furthermore, people that vote for policies that increase taxes are essentially saying they believe those who have more should either give more or be thrown in jail. Directly analogous to the man holding the gun to the soup cook's head, demanding he give his soup to the poor. Except that they don't even have the courage to hold the gun themselves.
Government legitimizes threats of violence as a valid solution to social problems, despite the fact that violence is the antithesis of peaceful negotiation. Government and peaceful society are anathema to one another.
Circling back to the violence of the "extreme" left, because of the leftist rejection of the non-initiation of aggression principle (and by extension their rejection of private property norms) doesn't that mean leftists exclude themselves from the protection of these moral norms? Put another way, because the left reject the principle of the non-initiation of forces, doesn't that mean initiating force against them is no longer immoral?