You’re simply not allowed to discuss moderation in public and therefore HAVE to discuss it in Private Messages (PM). Discussing moderation in public is not allowed for a plethora of reasons such as derailing the topic, having third parties (other users) take advantage of the situation and so on…
Constructive criticism is always allowed. Constructive criticism ON MODERATION has to happen in private where there will be a dialogue between the moderated person and the moderation team.
Hopefully this was clear enough.