When at school I learned about Kohlberg's stages of moral development, there was a nice example of a moral problem (something like the Trolley problem, but I think it was about stealing an expensive medicine to heal someone) where either side could be argued from each stage of moral development. For example, you could make a completely selfish argument for either side "I don't care about anyone's property" or "I don't care about anyone's health", but you could also make an abstract principled argument for either side "we should optimize for orderly society" or "we should optimize for helping humans" (simplified versions). The lesson was that the degree of moral development is not the same as the position on an issue.

If I look at the "rationality / postrationality" vs "Kegan's stages" using similar optics, I can see how people on different stages could still argue for either side. Therefore, one could "explain" either side as a manifestation of any of stages 3, 4, and 5.

If the Stage 3 is "socially determined, based on the real or imagined expectations of others", we could argue that people who use the label "rationalists" do it because they are in the Stage 3, and they believe that other "rationalists" expect them to use this label, so they follow the social pressure. But just as well we could argue that people who avoid the label "rationalists" (and use "post-rationalists" instead) do it because their social environment disapproves of the "rationalist" label. Both sides could be following social pressure, only different social pressures, from different groups of people. Maybe "rationalists" are scared that they could lose their group identity. And maybe "post-rationalists" are scared that someone from their social group could pattern-match them to "rationalists" and consequently exclude them from their group, whatever it happens to be (academia, buddhists, cool postmodern people, etc.).

If the Stage 4 is "determined by a set of values that they have authored for themselves", we could similarly argue that "rationalists" have chosen the rational way for themselves, in defiance of the whole society (rejected religion and mysterious answers, criticized education that teaches the teachers' passwords), and using reason as science as their guides they found people with similar values at LessWrong, thanks to Aumann's "great minds think alike" theorem. But just as well we could argue that "post-rationalists" have chosen the post-rational way for themselves, in defiance of the Less-Wrong "rationalists". People from both groups can feel like heroic lonely warriors in an ignorant world dismissive to their ideas.

If people in Stage 5 are "no longer bound to any particular aspect of themselves or their history, and they are free to allow themselves to focus on the flow of their lives", we could find supportive arguments for that, too. The zero-th virtue ("do not ask whether it is 'the Way' to do this or that; ask whether the sky is blue or green; if you speak overmuch of the Way you will not attain it"), internal criticism of LW as "shiny distraction" on one side; abandoning the "rationalist" label on the other side.

What most likely happens in reality is that both sides certainly attract various kinds of people. (And even according to Kegan, one person is often in multiple stages at the same time.) However, here I am going to break the symmetry and say that to me it seems the "post-rationalist" side is almost defining themselves as "we are in the Stage 5, and those who identify as 'rationalists' are in the Stage 4". At least this is how it seems to me from outside. (But complaining too much about this would be the pot calling the kettle black, because "rationalists" define themselves as "we are the rational ones, in the insane world". So in a karmic sense they deserved such comeback.)

Also, accusing other people of not being in Stage 5 feels to me like a kafkatrap. There is no way to defend against such accusation, because whatever evidence of being in Stage 5 you bring, can be dismissed by "Stage 5's never claim to be Stage 5's, so everything you said is evidence of you not being in Stage 5". (But it probably doesn't work the other way. If you admit that you are not in Stage 5, that statement will be taken at face value. At least I think so; I didn't actually try this.) So how does one convince others that they are in Stage 5? From observation, the solution seems to be having a blog about Kegan's stages, and judging others as not being at Stage 5 yet... if you do this, you establish yourself as an expert on Stage 5, and by definition only people on Stage 5 can be experts on Stage 5. If these are the rules of the game, I don't want to play it. (Note how I used the same cheap status trick here: defining other people as pawns in a system, and myself as the smart one who is above and beyond the system. Meh. Oops, I did it again. I am so meta I must be at Stage 8 at least. Oops, I am doing it again. I admit the game is a bit addictive.)

For me, the "rationalist" movement is a place where people similar to me can come and find each other. (Roughly defined as: high IQ, non-religious, trying to "win", willing to help each other, trustworthy, not interested in status games. There is probably more that I can't easily describe here; probably some clicking on personality level.) Even most people who come to LW meetups don't satisfy my criteria, but there at least I can find the few ones much easier than in the general population. I would be sad to lose this one coordination point. Meeting such people brings value to my life; I find it emotionally satisfying to talk with people openly about topics that interest me without having to censor my thoughts or explain long inferential distances; sometimes I also get some useful advice. At this moment I don't see any value I could get from "post-rationality", but I am willing to learn, as long as it doesn't feel to me as someone just playing status games, because I have low tolerance for that.

Kegan has published a lot of evidence

Thanks for the pointers. I'm more interested in validity than consistency here, I think.

Not very convincing

I was intending to inform, not to convince. (I agree that no one should be convinced of anything much by my saying that I mistrust some people's motives.)