Very interesting points. I am working with an organisation which relies on volunteers, and have experience too of working with the British Red Cross in an advisory as well as volunteer capacity. The point for me is that our volunteers help us put on trainings in life skills and personal development, and that means we deal with people who can have of vulnerabilities, from being mildly annoyed with their home or work life, to having more serious and long-term issues.
So, responsible organisations can't just let volunteers loose in these situations, and let them do what they think best. The Red Cross, for example, only lets people volunteer in key support roles after they have been properly trained. Even fundraisers operate under clear guidance. At a serious level, organisations like these operate within strong legal frameworks. Safeguarding is just such an issue, not just for volunteers, but for staff who work with volunteers (eg, the Oxfam situation in the UK right now).
Hence, I am looking for a way to ground our volunteers in our values and purpose, and to have roles and accountabilities which can be given as well as removed, while at the same time bedding-in a way of acknowledging and accessing the tensions as well as the energy from our community. I see the partnership model as a way to conceive of short-term, task-specific distributed authority arrangements, that last as long as an individual person is taking on a key volunteer role (where they become the role, not the person).
If there was no need to meet legal and ethical requirements with vulnerable groups, and if my organisation didn't have the vision and values it does, then I can see how volunteering could be much more free form. Definitely horses for courses, I guess, which is what I see as a strength of the Holacracy approach.
By the way, thanks for drawing out my thinking on this!