I don't quite understand what you mean here by the state being involuntary and anarchism being voluntary. If you point is that the minority would walk away somewhere if they disagree with the majority, I don't think this relocation will be by their free will and accord. Actually, they will be coerced to do so by the majority. It happens daily in life even without state and its laws. But exactly the introduction of state in the form of the law allows to break this otherwise circular argument...
Coercion
Threat of kidnapping, extortion, force or violence to be performed immediately or in the future
Lets say you're at a friend's party, and you don't like the party but you also don't want to leave. Are the party-goers now coercing you to leave?
At a friend's party I won't be in my own right by definition, so this example is not worth considering at all in the first place. Whatever answer I may give, I will be either logically wrong (correct answer with false reasoning) or factually wrong (correct logic based on false premises). Choose a better example...
Could I expect you throwing some light on what you meant by the state being involuntary and anarchism being voluntary?