Evil is if course subjective,
and influenced by perception. The psychopath not being able to understand his or her actions are evil is an interesting one. If they’re not mentally capable of understanding the difference between right and wrong would it even be legal to try and convict them?
As I said, IMHO an evil act is one that ddliberately causes unnecessary suffering, but from there we have to debate necessary. Is eating meat necessary for humans in developed countries in the 21st century, just as one example?
Yet as a meat eater I don’t view the consumption of meat as evil. Though subjecting animals we eat to unnecessary suffering I might consider to be unethical, like Halal or Kosher butchery for example, because more humane methods are available, but then I’m not religious so again it’s a subjective opinion.