The original Yvain's sin was admitting that hypothetically "his side" might be wrong about some details, and it might be worth to consider the evidence, and in case it shows convincing, update. Then he just dug himself deeper.
To a LW regular, this may seem like Rationality 101, but in real life, this is often enough to be expelled from the paradise of one's tribe. (And it happens in many different tribes, not just this one.)
The similarity between Yvain and neo-reactionaries is that both of them are willing to look at the evidence against Yvain's tribe's beliefs. They may have completely different motivation to do that, but whatever. This is what a loyal member of the tribe wouldn't do. This is what people in general don't do, unless they are exceptionally honest or exceptionally socially clueless.
I understand that your comment might exaggerate for the sake of irony, but I think you might be getting too close to applause-lights with it. You're saying (essentially) that it takes exceptional honesty to be willing to look at the evidence against your tribe's beliefs. That seems wrong. Complete and utter dogmatism isn't that common outside explicitly religious domains. People very frequently are honestly willing to look at the evidence against their wrong beliefs, and then they're honestly unconvinced by it, even if often it's because they misunderstoo...
A long blog post explains why the author, a feminist, is not comfortable with the rationalist community despite thinking it is "super cool and interesting". It's directed specifically at Yvain, but it's probably general enough to be of some interest here.
http://apophemi.wordpress.com/2014/01/04/why-im-not-on-the-rationalist-masterlist/
I'm not sure if I can summarize this fairly but the main thrust seems to be that we are overly willing to entertain offensive/taboo/hurtful ideas and this drives off many types of people. Here's a quote:
The author perceives a link between LW type open discourse and danger to minority groups. I'm not sure whether that's true or not. Take race. Many LWers are willing to entertain ideas about the existence and possible importance of average group differences in psychological traits. So, maybe LWers are racists. But they're racists who continually obsess over optimizing their philanthropic contributions to African charities. So, maybe not racists in a dangerous way?
An overly rosy view, perhaps, and I don't want to deny the reality of the blogger's experience. Clearly, the person is intelligent and attracted to some aspects of LW discourse while turned off by other aspects.