It takes an idiot to be cruel.
The best leading indicator of intelligence is kindness. Back in caveman days, if you saw something new, and you weren't scared of it, you got eaten. Or worse. That's evolution. Our base instinct is to react first out of fear. It takes intelligence to overcome that first base programming and seek a second, more understanding, more tolerant reaction to new things. In evolutionary terms, it was our intelligence allowed humankind to develop empathy for one another. It is the foundation upon which all civilizations are built.
You want to know who the smartest people in the room are? Look for the kind folks. Look for those who help others. Look for those who give selflessly, thoughtfully, of their time and skills and talents.
Conversely, you want to know who the dumbest dumbasses who ever dumbed are? Look for the people whose entire lives are marked by acts of cruelty.
