More or less, for better or worse, think of the mods as the refs. You are limited in criticizing them, especially publicly. They have authority and it's not to be questioned. You can only go at one and complain so long before you're hit with discipline.
Now, given the utter blanket claim to irreproachable "authority" claimed, the context of which I received this PM should be irrelevant, but I'll be glad to provide the details if asked.
My point, however, is this - I hope this isn't the instruction, directly or indirectly, your moderators are "performing" their duties under.
First of all, let me break down the analogy.
Sports refs ARE given disciplinary authority over players, but their powers are not arbitrary and are clearly defined and known to the players.
Secondly, the sport of disciplinary powers is that so arguing doesn't take focus and time away from the games. Given that the sole purpose of RealGM is DISCUSSION, to argue that users can't openly discuss criticism of mods, is to argue mods are above the very reason the site exists.
When exercised in this manner, the disciplinary authority serves no purpose other than self-service.
So I'd like to ask a genuine question - do the mods serve the users of this site or do the users serve the mods?
Because one mod has told me directly they are above reproach, though no offering explanation as to why this is to the betterment of the site and suggesting quite plainly that they don't like to be questioned and will use their "authority" to place themselves above it.