There are gains from cooperating with as many others as possible. Maybe these and other factors outweigh the risk or maybe they don't; the lower the probability and extent of Lovecraftianity, the more likely it is that they do.

I agree that "probability and extent of Lovecraftianity" would be an important consideration if it were a matter of cooperation, and of deciding how many others to cooperate with, but Eliezer's motivation in giving everyone equal weighting in CEV is altruism rather than cooperation. If it were cooperation, then the weights would be adjusted to account for contribution or bargaining power, instead of being equal.

Anyway, I'm not making any claims about what to do, I'm just saying people probably aren't as Lovecraftian as Roko thinks, which I conclude both from introspection and from the statistics of what moral change we actually see in humans.

To reiterate, "how Lovecraftian" isn't really the issue. Just by positing the possibility that most humans might turn out to be Lovecraftian, you're operating in a meta-ethical framework at odds with Eliezer's, and in which it doesn't make sense to give everyone equal weight in CEV (or at least you'll need a whole other set of arguments to justify that).

That aside, the statistics you mention might also be skewed by an anthropic selection effect.