My understanding of Michael Vassar's position is that the people who are dissuaded from thinking about existential risk because of remarks like Eliezer's are too irrational for it to be worthwhile for them to be thinking about existential risk.

Seems like a reasonable position to me.

Really? I don't understand this position at all. The vast majority of the planet isn't very rational and the people with lots of resources are often not rational. If one can get some of those people to direct their resources in the right directions then that's still a net win for preventing existential risk even if they aren't very rational. If say a hundred million dollars more gets directed to existential risk even if much of that goes to the less likely existential risks that's still an overall reduction in existential risk and a general increase to the sanity waterline.