Our caveman/cavewomen brains think that we will only ever interact with a very small number of people, and losing the respect of anyone could materially worsen our chances of survival in a crisis.
Determining for how many people that caveperson assumption is valid is difficult, since their lack of support network-building ability also makes them easy to overlook. Such people do exist, however, and I would not be surprised if they appear at higher frequencies among marginalized demographics, especially the sort that would otherwise have interest in communities such as LessWrong.
I doubt that the author of the linked article is in such a situation, however; when a blog post directed at one individual gets linked at a larger community blog and receives >70 comments discussing it and its message, my prior probability for "someone with an unstable social network and an inability to repair damage to said network" is adjusted way downward.
I don't think laboring under ancestral-style social assumptions necessarily implies a weak or unstable social support network, or problems maintaining social links. Particularly not the latter; if you're working with a set of unremediated instincts telling you that losing rapport with anyone in your ingroup is a disaster, then it follows that you should invest heavily in repairing any damage to it.
It does suggest some failure modes that wouldn't be present in the network of someone more willing to burn bridges, but we're talking differences in style and overall optimization, not being strictly worse at everything social.
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.