Something like 95% of LWers self-classify as social liberals.

Regrettable! I'd hope more would have the good sense to be Communists ;-).

Why would such a phenomenally non-socially-conservative group fixate on neoreaction unless it had some surface plausibility?

Because people are often attracted to things which offend them, like Republican Senators and homosexual prostitution ;-). This is pretty obvious if you model LWers as human beings rather than Bayesian utility maximizers.

That neoreaction uses bits of LW argot is probably more relevant, but it's hard for me to imagine it being the whole explanation. Would a serious creationist last long here just because they larded their comments with our jargon?

That depends. Was he once a spokesman for the Singularity Institute?