I think both you and Eliezer are right. Eridu probably is sincere in his beliefs, but also has been reinforced by the attention he received into provoking people in a way that doesn't help his cause. He seems to even know this but still endorses his behavior:

I knew what I was going to get when I posted my first comment -- I just thought it'd be an amusing waste of my time, which has been roughly the case.

ETA: I'm not sure how we can try to help someone level up their rationality without at the same time giving them attention and risk turning them (by reinforcement) into a troll. The "hide downvoted threads" mechanism only limits the damage...