There is nothing wrong with being polite. There is much wrong with not being polite.
Yes. But that's not the argument. You rendered it as if the moderators would step in and act somewhat opaquely - the members need not agree. The reality is that they should, and probably will, act according to published rules which we are all aware of. Like a government, and as imperfectly. -------------------------------------------------------------------
There is no argument unless you are trying to pick one. I render nothing on behalf of the moderators. I speak only to the issue of civility as guests in their "house".
In your house, others are expected to be polite and abide by the "rules of your house". Suppose you don't utter curses in your home. Then, a guest did. You may ignore it at first thinking it was a 'slip', but after a while curses started flowing. When you call them out, they reply with "Show me where cursing is forbidden in your acceptable guest policy". Absurd, right?
We are all guests here. The moderators will (and should) step in and moderate anyone they feel (yes, as imperfect humans) is endangering the health of the list. The moderators are under no obligation to explain themselves to others. It is their house.