Calling those who are extremely intelligent but "evil" broken or brain damaged is not true in most cases. In the entirety of Human history, the most evil have rarely been brain damaged. Many lacked empathy, yes, but many had it in droves. There's a reason even the people at the top of Nazi hierarchy refused to use direct terms referring to mass murder, even in closed doors with life-long friends who were entirely on the same page. The vast majority of people are empathetic, they require dehumanisation to conduct terror. There is no lack of empathy when your fellow man is no longer seen as Human, there is simply a lack of value. Something without value deserves no empathy. We empathise with animals, each other, or even inanimate objects in some cases because they have value, whether that's due to the love of family, love of friends, the material value an employee can bring to a business, the "innate" value of your fellow man (which is in no way universal nor equal among each member), the value of cute animals, etc. You'd have to explain why intelligent people with zero issues have a disgust at seeing a dog in pain but have no issue watching gazelle eaten by lions.