Some of it is 
I’m not sure what you mean by this. It’s not an either/or situation 
Let me turn it around - what do you think we gain by being private? I think defaulting to open is worthwhile, especially for the calendar.
100% agree with this being volunteer-centred, and I think that means keeping invite-based signup for now. I do want the public to be able to sign up one day, but not until we have a healthy core of volunteers & organisers driving the main needs of the forum. I think the next step for that is to allow existing members to invite more people themselves (instead of having to go through staff members like me). We’ll get to that shortly, I think.
However, to even get them to be involved it has to seem like a good idea - and right now (for example) if you view the calendar while not logged in, it appears empty (because the events are private). That’s not a good look for trying to encourage more groups to use this, hence I’d like to give them a way to see what’s going on. (This also relates to stuff I discussed in person yesterday but I’ll do a trip report for that in a bit).
So far, I’m seeing 3 +1s (4 if you include me) and one -1 on this (perhaps I should have done a poll), so I’ll get that sorted over the weekend.