One of the biggest problems of both left- and right-anarchism is that the notion of "voluntary cooperation" is extremely philosophically problematic.
Now, I definitely want to act cooperatively, i.e. I don't want to steal from people. I don't want to hurt or kill other people. I don't want to endanger other people. I don't want to have non-consensual sex with other people. I don't want to exploit or take advantage of other people. I don't want to enslave or otherwise subordinate other people. That's just how I roll. But what does it mean to say I want to refrain from these activities, i.e. that I don't want to do these things?
Let's take a more scientific approach and consider an operational definition of "wanting". If I were given an externally unconstrained choice between two societies, one of which (for whatever reason) theft, assault, murder, rape, exploitation, and slavery were rare, and another where these activities were common, I would choose the former, the society where they were rare. But that definition doesn't tell you anything about my wants or desires, it just tells you that I'm rational: By any reasonable metric, I will be materially and physically better off in a society where theft, etc. were rare... even if subjectively I were to have no particular desire to act cooperatively. So framing "want" in this sense doesn't help much.
Let's try a slightly different frame, again a choice between two different societies, both of which are about equally cooperative. In the first, people act cooperatively (i.e. they don't steal, etc.), but there are no physical or violent constraints: that's just how the individuals in that society happen to roll. On the rare occasion where someone does steal stuff, or assault someone, etc., they just shake their heads and say, "How regrettable." In the second, people act cooperatively, but there are physical and/or violent constraints on uncooperative behavior. (I'm of course excluding the middle of a society with nonviolent constrained to cooperate; more on this in a minute.) Superficially, I would prefer to join the former society and act cooperatively; they sound like genuinely nice people. Because of the violent constraints on cooperation, I really don't know anything about the character of individuals in the second society. The problem, though, is that there are a lot of assholes who would see the first society as ripe for exploitation: They would join the first society just so they could steal, assault, murder, rape, and enslave its members... including me. (What if there were no assholes? Again, more on this.)
But there's a substantial problems with the second society too: I really can't be sure the physical, violent constraints on cooperative behavior won't be employed "uncooperatively"; I don't know that the government (the institutions that physically enforce cooperation) won't turn into a "state" (according to Lenin's definition) to implement the oppression of one class by another.
What we have here is the Prisoner's Dilemma. It's "obvious" that everyone is better off if everyone cooperates than if no one cooperates. But it's equally "obvious" that if everyone else cooperates, an individual (with no external constraints on his behavior) is even better of if he himself does not cooperate: He gains the benefits of everyone else cooperating, but avoids the costs of his own cooperation. It's a perplexing conundrum; the problem itself is obvious but the answers are most definitely not obvious.
Let's look at some of the possibilities I glossed over earlier.
What if there were only "nonviolent" constraints on cooperation? Suppose, for example, that a person who stole, assaulted people, etc. were somehow shunned, ostracized, or something like that. The society would have to be absolutely nonviolent; if you can allow someone to starve or freeze to death for any reason, you might as well just shoot them. And even "minimally" violent constraints do not escape the philosophical problem: Omelas and The Country of the Kind both employ violence to preserve social cooperation. I'm all for efficiency, but using as little violence as possible is a horse of a very different color from refusing on principle to use any violence at all.
But if there are really only nonviolent constraints on cooperation (assuming there are those who must be constrained, see the next paragraph on "no assholes"), then what's to prevent the people "nonviolently" constrained from banding together to act as an exploiting class, to gain from each other the benefits denied by the rest of society? That's been the behavior of every ruling class in history: They really don't care that the hoi polloi hold them in contempt or refuse to socialize with them, so long as they obey. And they have always found soldiers and police willing to do the dirty work of maintaining obedience.
What if there were no assholes (or few enough that they could not band together to form an alternative society)? That's the most promising possibility; assholes are definitely not logically necessary, and I can imagine circumstances where assholes were as physically impossible as a human being born with working tentacles instead of arms and legs. Indeed, if such a society were to exist, I would join it... if they would let me in. The problem is that I have absolutely no idea how to arrange circumstances such that assholes really were physically impossible, except by the painfully slow evolutionary process of violently selecting out the most egregious assholes. We might get there in a thousand years, or ten thousand, or maybe even a million. (Why not? We have at least a few billion years to play with.) And when we do, good for us.
But as desirable as conditions might be that made assholes physically impossible, I don't see any practical way of arranging such conditions today or tomorrow. However technically correct one might be, I don't see much point complaining that we have a violent society, a lot of assholes, and (correctly) denouncing any attempt to contain them as perpetuating the violence of modern society. A journey of a thousand miles begins with a single step, and a project of a thousand generations begins with the work of a single lifetime. I may not be able to achieve anything within shouting distance of perfection within my lifetime, but I would like to at least get a step closer.