Out of curiosity, what is the fraction of LW posters that believes this is a genuine risk?

Vanishingly small - the post was deleted by Eliezer (was that what, a year ago? two?) because it gave some people he knew nightmares, but I don't remember anybody actually complaining about it. Most of the ensuing drama was about whether Eliezer was right in deleting it. The whole thing has been a waste of everybody's time and attention (as community drama over moderation almost always is).