The issue that I feel lies behind much of the conversation on this subject (but which I don't think I've seen explicitly outlined) is that of the governance of the organisation. As this is very much a project founded on the idea of community, is there to be some kind of accountability of the board to the community?
The board is legally accountable to the guarantor members. They get a vote at AGMs and can elect a new board if necessary.
How many members of the company do you anticipate there being? Will making someone a member of the company be a regular occurrence? What rights will supporting membership bring?
I don't think supporting members have any legal rights. I think the idea is for guarantor membership to be handed out to any supporting member that wants it (and is over 18, and whatever other legal requirements there are). The issue is with handing it out to people that aren't supporting members, but hopefully that's just a temporary glitch!