To start out I agree with you that in a perfect world all interactions would be voluntary and there would be no government. However, we don't live in a perfect world. You had a lot of good examples, but let me give you another. Let's say someone's property is land locked. No one surrounding will let them on their land. Not letting someone on your land is not immoral, so no one is doing anything wrong and yet the situation is still untenable.
Now you mentioned having something like an HOA resolve disputes. But what if someone won't follow the HOA rules. You take them to court. But what if they don't follow the courts ruling. The police come. And that is why HOAs work. Ultimately they have the government backing them.
People will always have disputes, and some one will always need to not only mediate disputes but have the ability to use force to back up their authority.
Having said that I think government is horribly inefficient and will always be out performed by the free market. So we should have as little as possible.