It's an exaggerated version of how (e.g.) some women or black people might feel on coming to LW and finding (e.g.) people vigorously defending the idea that it's perfectly sensible for an otherwise identical job application to be viewed as evidence of lower competence if it comes from a woman, because women are so much less able than men that all the other information on the application doesn't screen off sex from competence. Or writing in a manner that simply takes it for granted that black people are unintelligent and prone to crime.
I repeat, it's an exaggeration. I'm pretty sure fubarobfusco isn't claiming that there are actual demographic groups that are actually seriously regarded by a lot of LW people as non-persons or fit objects for torture. But I think it's entirely defensible to say that some real demographic groups are likely to experience something similar in kind, although distinctly less in intensity, here, and to be concerned that that will produce an effect similar to the one fubarobfusco describes.
Or writing in a manner that simply takes it for granted that black people are unintelligent and prone to crime.
If someone can't distinguish between a categorical statement ("all demographic X people have trait T") and a statement about statistical tendencies ("the demographic X average for trait T is N standard deviations below that of demographic Y") , I question their ability to contribute to any community that's based around rigorous thinking.
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.