> but it's not plausible to think that the answer is "one side is good and has good views and sees HN accurately, while the other side is bad and has bad views and sees HN completely the wrong way".
it’s not clear to me why you don’t think this is plausible unless you take the centerist position that all political extremes are equally wrong. It’s not like that would be a crazy point of view for you to hold. However, you seem to either deny holding it or deny that you are appealing to it as part of your argument.
> it's not plausible to think that the answer is "one side sees HN accurately, while the other side sees HN completely the wrong way"
The reason it isn't plausible is that the claims the various sides make (specifically about the ideological bias they perceive in HN, and in the mods) are so interchangeable—they resemble each other perfectly, except for one bit (the ideological polarity) flipped. It's possible that radically different mechanisms could be producing these isomorphic comments—wildly distorted perception in one case, accurate perception of reality in the other—but it's not plausible.
Suppose I come out of my house in the morning and the street is wet. Most likely it rained last night. Now what are the odds that most of the street is wet because it rained, but the stretch right in front of my house is wet because someone came out with a hose and watered it? That is possible, but not plausible. It's more likely that a common mechanism explains both, especially because there's a simple explanation for what that might be (that it rained).
I'm sure that's not the best analogy, but it's the first one that occurred to me (well, the second), and I can modify it to make it even more analogous to the situation on HN.
Consider that two neighbors are each convinced that while it rained on their neighbor's stretch of street, their own stretch is wet because someone came out in the night and watered it. It's possible that one neighbor is assessing reality accurately while the other is totally wrong. But it's not plausible. It's more likely that some common underlying mechanism is producing these perceptions, which are identical except for the obvious you/me bit flip, and which can't both be true because each claims the other is false.
> However, you seem to either deny holding it or deny that you are appealing to it as part of your argument.
It's the latter. The reason this is not an argument in favor of political centrism is that it's not an argument about the underlying politics in the first place. It's an empirical argument about the comments people post. These comments are so identical that it is not plausible that one mechanism produces half of them (or whatever the portion is) while a radically different mechanism is producing the other half. It is far more likely that a common mechanism is producing them—especially because there's a simple explanation for what that might be.