I'm convinced it's worth actively discouraging them from participating in LessWrong
Really? From a thread devoted to increasing the diversity of LW you managed to conclude that people with political views sufficiently different from yours should be driven away from the site. Do you want another echo chamber? There are plenty of those on the 'net.
Now would be a good time to re-read Well-Kept Gardens Die By Pacifism in its entirety.
Now would also be a good time to re-read Politics Is the Mind-Killer and ponder on the difference between trolls and people whose political ideas you don't like.
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.