It's not clear to me that avowed racists (and sorry, that's what "HBD" is a euphemism for) make up any any significant portion of the LessWrong community, just a loud portion of it. Self-described "reactionaries" are certainly a very small (but loud) minority here.
Really we should get better at conveying when opinions held by a loud minority here are not by any means the opinion of the majority.
What do you mean by racist?
Edit: If by racist you mean "hate people who don't share the same skin color with them" then I would guess that there are almost no racists on LW.
If by racist you mean "think that some racial groups are superior and others inferior" then I would also guess that there are almost no racists on LW.
If by racist you mean "think that different populations of people differ significantly along various axes such as athletic ability, intelligence, memory etc." then yes there are a lot of racists on LW.
The third option does not imply either of the first two.
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.