What people call "obvious biases" are typically what they themselves are choosing to select out of the statistical cloud of posts that get made here. The bias at work in making such a selection is one's own, but we project it onto the community, and then create a superior image of ourselves by posturing above it, which is what I mean by supercilious. This is a drama between oneself and oneself, which has nothing to do with real conversation. It's a way of changing the subject to oneself. To be fair, you're hardly the only one doing it; it's quite common, but I have to tell you that it tends to be low-quality commenters who do this.

It frequently comes with labels like "echochamber" and "groupthink", which are also ways of elevating oneself as the noble freethinker standing against the mob, or some such image. Actual noble freethinkers never behave like this, so the whole thing is incongruent—it's simply a way of flattering oneself, which (ironically, because we all feel so unique) is one of the most repetitive and tedious things that people do. That's why we shouldn't do it on a site that's trying to have interesting conversation.

Another angle: people seem to posture above the community when they feel like they need to defend themselves against it. Presumably they want to defend themselves against some claim of i-am-very-smartness that they feel is emanating from the community, so they puff themselves up and put the community down by way of compensation. In reality, though, no one is making such a claim. HN isn't making such a claim—HN isn't a person to begin with—and certainly the people running HN are making no such claim. It rather arises in the psyche of some readers, for whatever internal reasons. The internet can be crazy-making that way.