Should "truth is a defense" be a maximum rather than a minimum protection?

Professional associations have rules of conduct among members that restrict whining about fellow members. By joining, voluntarily or as a mandatory prerequisite to an occupation, are members obtaining the right to tell other members to shut up? Well, yes. Is it right?

Members of a particular professional association are uniquely qualified in the topic matters, and are uniquely "in the loop", thus they would be in the best position to effectively criticize fellow members.

Maybe we should have a BPB, Better Professional Bureau. I recently helped someone post a complaint online to the BBB and they got a rather fast and complete resolution to the issue. It was a great experience for them, I anticipated the ultimate result, but not the surprising speed of the conclusion . .