I haven't made up my mind on whether civility or credibility is more important for a moderator. For most forums, I would lean towards the former, although given the nature of SDF, I can see how this could be an exception. Other than that, I don't disagree with what you said.Civility is all well and good, but it comes second to credibility in my book. There is certainly no shortage of fools—in any language—going around making wild claims without anything close to the required evidence. In my personal opinion, the mods are far too lenient when it comes to tolerating such nonsense. I can go to many places to read nationalist nonsense—again, in any language—but there are only a few places with as much value-add as (some) SDF contributors.
Again this is just my opinion, but if folks have nothing of substance to contribute then they should just learn how to shut up and listen. And no, speaking Mandarin does not qualify as any special talent; there are well over a billion of us, and plenty here who don't editorialize their translations beyond all reason.
What I like you to consider is that there is actually no trade-off between civility and credibility. One does not come at the expense of another, and you can be civil and credible at the same time. The language and actions of moderators impact on the reputation of forums, for better or worse.
Other than that, again I stress I don't disagree with what you said.