In a successful forum, there are two components:
a) what people strictly don't do (enforcement of rules);
b) what people strictly do (a purpose for sensible actions).
The part b) is much more important, as without it, a) makes no sense at all.
So, the b) part is instrumental to the success or failure of any forum.
The WRF team seems to be fully aware of this. In fact, they seem to change the part a) rather freely according to the circumstances that influence the part b), although they do indeed very strictly proceed with a) in any given state.
So, what does the part b) depend upon? It often happens that one avoids to say something not because it would have been forbidden by rules or is strictly out of place, but because it wouldn't be a sensible thing to say given the purpose of the discussion. And it's rightly so, because the person himself is the best judge for sensibility of his words, anyone else's judgement would have been poorer because they don't share his internal thoughts and do not have his personality, they don't have the means to know what he really means.
So what the WRF team seems to be doing is just one thing that works in our difficult world: to keep the purpose as narrow as possible. Because otherwise, the air of modernity, the modern culture doesn't have any good means to tell a good purpose from a bad one, not any socially accepted means at least. If a person has such means for themselves, then they are a good person, and that's it, but socially, good people are always overwhelmed by bad people unless the purpose is being kept very narrow so that one can rely on social standards for the feelings of right and wrong rather than on personal ones, which are supposed to be a much more fine work with usually no social consequences. While the standard of narrow action is socially familiar to people, so it can be expected to work in a wide society, and it does indeed work.
The moderators are very keen in their phrasings, and that's exactly the thing which is most important for the part b). What do they constantly — not really 'say' — imply? "If your observation enriches the dictionary entry, then feel free to say it; otherwise, there's no use". And it makes much more influence on the climate of the place than any prohibitions, which only make sure that the part a) is also upheld, and those who don't feel the spirit of the place do not contribute.
So, whatever statements can be made on ethics of the standards of banning here, the point that these standards are beneficial to the spirit of the place holds true, in my opinion. And it's very important, in my view, a successful cultural project with a huge organisational component in a world where such projects are a rarity to be desired. Business is no democracy, and so is culture…