In the comment section of Jim's Blog, Toddy Cat pointed out some positions he saw as areas of agreement between Yvain and neoreactionaries (Jim himself disagreed, and Yvain has not responded as far as I'm aware).
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 ...
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.