It puzzles me when people say such things. We don't have a truth meter [1]; how are we supposed to decide what's true vs. false? By definition, there's zero consensus on any contentious topic. Should we pick one view and impose it? Whose would that be? my own? Even if I thought I knew the truth about everything (and I am very far from feeling that way), I can tell you how well that would go over: everyone would hate it.
There's another level too: are we supposed to ban people for being wrong? Being wrong is part of finding out the truth; of being curious. No one makes it to the truth in a single jump, nor on their own. We need to be allowed to be wrong sometimes.
And another level: HN is about intellectual curiosity and interesting conversation. Interesting conversation is not always a pure sequence of true statements. Curiosity wants to figure out the truth, of course—but optimizing for curiosity [2] is not the same thing as optimizing for truth. The latter would mean excluding speculation, for example. That would be less interesting!
When someone wants the mods to decide what is true and moderate by that, I can't fathom what they mean, unless they just want moderators to support whatever they agree with and ban whatever they disagree with. No one would put it that crudely, but no one has explained what else is being advocated. One needn't consider this for very long at the general level (i.e. the level of the entire community) to realize how it could never work.
The very people making this point about the "contents of the vessel" would be at each other's throats if one asked them to declare what the truth actually is, since the first thing they'd discover is they have wildly differing views of it. That's why this point can only be made, or agreed with, in the abstract. The moment you cross into claiming any specific truth about a contentious topic, others will immediately protest that it is not a truth at all and that the opposite is true.
Figuring out the truth is a social process—it happens by discourse, communication, exchange. This is everyone's job together, not some special power of the admins. The admins' job is to facilitate that process. This does not involve declaring what the truth is and imposing it on those who disagree, any more than it's a referee's job to decide which net the ball or the puck should go into.
[1] https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
[2] https://hn.algolia.com/?dateRange=all&page=0&prefix=true&sor...