I'd like to raise another form of interference that sits poorly, at least with me.
Audiogon prohibits sharing personal contact info. I find this pretty intrusive: the only possible reason i can think of is to avoid them losing commissions on sales. Yet most discussion here is non commercial.
It can lead to the absurd as well: I recently received a PM asking for a schematic or help on making a LPS. I replied, and along the way added "and you can buy generic circuit boards on <<that auction site>> that are easily modified and make the task easier". Mistake. It was blocked and is awaiting moderation. Really?