There's no HARM in making it "opt-in", as has been done,
if that's what (some) people want, but personally I don't see the point. All it means is an extra click, one-time, to opt into it. Before you do that, you still see it, it's just got the word 'private' next to it. You presumably would still see its threads in 'new posts'.
If some people want moderation, and some don't, then why not set up two soapboxes, one moderated and one not?
Or ones with different degrees of moderation, and when I say 'different degrees' I don't even necessarily mean that on linear scale - i.e. one could have moeration to the point that only 'intelligent debate' is allowed (I'd be the obvious choice of moderator for that one
), one where no swearing is allowed but anything else goes, one where personal insults are banned but swearing is encouraged, etc etc.....