Many of the Nazis convicted at Nuremberg were undeniably smart in the sense that they could perform abstract reasoning better than most people. Some of them had top 1% IQs and none of them had below average IQs (yes, IQ is an imperfect measure of intelligence, but at the same time, anyone who gets a 130 on an IQ test is smart...
They just might not be smarter than someone with a 120 or a 110 from a different background).
I've had a long (25 years so far) and successful career in computational science/engineering. Everyone I have worked with in the last 25 year, with only 2 exceptions I can think of, was smarter than most people. I have heard some truly awful things come out of coworkers mouths. Particularly in the run up to the invasion of Iraq. People who could write software that accurately predicted airflow through jet engines who did not care that the people of Iraq were not the same people who attacked the WTC. They knew, but did not care! They simply wanted to lash out at brown people in the middle east.
Even "Smart" people are pretty stupid and make mistakes all the time, and most don't respect truth enough to self correct. Empathy is a decision, and making that decision requires being able to make correct choices.