I agree with you; I am abusing terminology.

For the record, though, I do think we have a bias against theism in the sense that you've described. I understand why LessWrong might choose to consider the "does God exist?" question settled, but we go further than that. We frequently discuss how terrible religion is, and applaud efforts to promote atheism, despite the benefits to happiness etc. that religion provides.

I think it's understandable that we have such a bias. On LessWrong, we value truth and truth-seeking; this goes far enough that it's almost a moral value. When other groups actively discourage truth-seeking, we oppose them.

I don't know anything about social psychology, but my experience with other social sciences suggests that liberal, humanist values are deeply ingrained in their system. What I mean is, the social sciences are not just truth-seeking engines looking for facts about humanity. They have their own moral values attached (e.g. reducing discrimination).

Just as we on LessWrong are reluctant to engage in discussions with people who oppose truth-seeking, social scientists may be reluctant to engage in discussions with conservatives, because conservatives tend to hold moral values that are actively opposed to the social sciences' agenda.

This article suggests implicitly that the social sciences should be about truth-seeking, not about promoting some political/moral agenda. The willingness of social scientists to admit their bias against conservatives suggest that they feel otherwise.