"If the state did not exist private property owners could mow them down with machine guns."

Just to clarify before anyone freaks out, I was engaging in a bit of hyperbole here. Property owners in an anarcho-capitalist society should of course try to ward them off with fences or walls or tear gas or some other non-lethal means first, but of course if that does not work and the situation escalates, deadly force to defend property rights could become necessary.