Conspiracy theorists, evolution deniers, religious fundamentalists, alien abductees and so on are examples of people getting together, and successfully rationalizing their belief in some quite twisted ideas. We don't call such groups "smart people", typically. They're not necessarily stupid either. They're just people.
So it's just the "curse" of being a human, I guess.
Whether we use our mind superpowers for good, or in order to fool ourselves and the people around us is completely independent of one's smartness, and has more to do with wisdom.
Many people believe that if you can wrap a convincing narrative around a set of selected facts, the narrative must be truth itself. Stories posing as insight are all around you.
Experience leads to wisdom, and wisdom teaches us to be more open-minded and less sure in the stories we hear or tell ourselves.