I'm at a loss regarding what you must consider 'horrible'. About the worst example I can think of is the JoshElders saga of pedophilia posts, and it only took two days to downvote everything he posted into oblivion and get it removed from the lists - and even that contained a lot of good discussion in the comments.
If you truly see that much horrible stuff here, perhaps your bar is too low, or perhaps mine is too high. Can you provide examples that haven't been downvoted, that are actually considered mainstream opinion here?
Most of these are not dominant on LW, but come up often enough to make me twitchy. I am not interested in debating or discussing the merits of these points here because that's a one-way track to a flamewar this thread doesn't need.
The stronger forms of evolutionary psychology and human-diversity stuff. High confidence that most/all demographic disparities are down to genes. The belief that LessWrong being dominated by white male technophiles is more indicative of the superior rationality of white male technophiles than any shortcomings of the LW communi
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.