I defnitly have a diffrent interpretation of voluntarism. I rather understand it as the freedom to act as I want to and supporting others in their opportunity to do so.
Also anarchism as Emma Goldmann describes it is order without authority. To have order a society needs a medium to conclude on a set of rules. So even when it is not a state, a constitution would even exist within a perfect anarchy.
And by what way somebody can be held accountable by commonly accepted rules as property rights, when there is no legitimate entity to enforce it?