Yes, I can see that abusive emails and private messages could be very upsetting.
I presume, though obviously I don't know, that the people who indulge in this sort of thing are 'active' participants in the forum that causes them upset. I suspect they might not find their behaviour so satisfying if they were on the outside of a Private Forum 'looking in' but not being known by the particpants to be there at all.
DB makes the point that disputes will simply migrate to another, public thread. However, I don't see that as any more problematic than it is already. I guess if Roberto had joined DB's private forum, their spat would still have occurred.
DB's other point about the unwillingness of some posters to post in public what they're already somewhat shy of posting in private is undoubtedly true. Feeling safe is a problem everywhere in life. Personally, I'm not sure this is an adequate enough justification for the existence of 'closed' private forums; but others, including DB, may feel differently.
On the question of "information beggars", doesn't that include all of us? I mean, what can our purpose possibly be anywhere online if not to glean something we don't already know from those that do, or to disemminate what we do know to others? If I don't know enough about trading to reciprocate on this forum, there are subjects I know a lot more about that I gladly give of my time freely to assist others elsewhere. I find the whole business of sharing knowledge in this way fantastic. In my own area of expertise, I would hate to find myself distinguishing between those I considered worthy of my nuggets of wisdom and those I didn't. Or to limit myself to communication only with my 'peers'. However, I would certainly exclude, assuming I could, as far as possible, "detractors, interruptors and other nuisances".
I used to post a lot on another forum associated with some work I do. I ran into problems with over enthusiasm which resulted in me firing off far more posts than were justified. So I reined myself in by saying I was taking a sabattical. I couldn't believe the number of emails I got from people I had never known existed saying how much they had enjoyed my posts and would I reconsider.
Now, the point of this story isn't to underline how wonderful a fish I am in one of the unlimited number of miniscule ponds the internet has spawned, but to point out that generally speaking readers exist in far more profusion than contributors; and we can have no idea what they are or are not getting out of what we write. I decry 'closed forums' for this reason more than any other.
I am all in favour of iron clad moderation, though. In fact, I think it's a prerequisite, these days.
Dod