Well, yeah, I agree that the state makes it possible. The system couldn't exist outside of the context of a coercive authority forcing compliance. But hey if market distribution can exist outside of a coercive state system I wouldn't have problem with it. I'm just not so sure that it can.
Basically the idea is that it doesn't mean much to be free of state control if you are being controlled economically. So to remedy the situation the possibility of economic exploitation must be removed from the equation. The state is merely a tool of the ruling class to enforce it's will on the captive classes. State socialism is an attempt, at varying levels, to employ the power of state authority to enforce progressive dictates. Now, I can certainly agree that, historically speaking, state socialism has pretty much been a disaster. I personally see socialism and statism to be at odds with each other.
You should read Kroptkin's "Conquest of Bread" or Marx's "Capital". Both give excellent analysis of how exploitation of one class by another began, with the concept of private property and how it is expropriated from the commons, and how that concept subsequently developed into feudalism, then capitalism.