My recollection is that the "don't post private messages" rule was made up by Matt several years ago, and in light of recent events maybe it is time for the site to give this irrational rule a second look.
As between two people, a conversation is only private if both sides agree to keep it that way. If you can't handle transparency, then be careful what you say.
If someone sends me a threat, or an offer to break the law, or a racist joke, I may want to let the community know.
Put another way, what interest does InvestorsHub have in creating a safe haven for secret messages about stocks . . . or anything else? I hope and assume that the answer is "none."
If a site that is devoted to a heavily regulated and oft-manipulated industry is going to have a rule, shouldn't the rule favor openness and transparency, or AT LEAST allow it?