Not all high IQ people are moral, but high IQ people are more likely to empathize, to understand the benefits of cooperation, and to the see the future more clearly.
In the 2014 movie, A Most Violent Year, about an immigrant family in New York in 1981, the protagonist goes to buy valuable property from a high IQ Orthodox rabbi who displays considerable empathy: “My people have gone over your books. I know this is a great deal of money for you. Why do you want this polluted dirty piece of earth?”
“I inherited this property from my uncle… This place can do nothing for me. I offered to lease this property to you for a fair price but you’re not interested. Why?”
“You have only 30 days to close the transaction. No extensions, no contingencies. If you fulfill the contract, the property is yours. If you don’t, we keep the money… I like you but the only reason we choose you is because of the favorable conditions of the contract.”
I’ve never had a shul rabbi with a lower IQ than me. You’ll notice that in all priest, minister, rabbi jokes, the rabbi always comes off the smartest and most pragmatic.
Morality depends upon empathy which depends upon the ability for abstract thought. Higher IQ people have more ability to think abstractly and empathically. They have more ability and inclination to place themselves in the shoes of others. They’re more likely to look for win-win solutions.