I hope to formalize my thoughts on this in the future but this is precisely my hypothesis- that as a whole we have reached peak intelligence; any smarter and we will start "seeing" the futility of life and just be more prone to suicide or other acts. It can also go the other way where no fully intelligent individual sees the need to cooperate and you end up with a lot of extremely selfish intelligent individuals killing each other.

I also think that's why traits like intelligence are not completely genetically determined within our species. It looks like evolution has programmed stochasticity into intelligence so that the distribution is kept intact within the population while no individual lineage gets an unfair advantage.