Any example I could give could be disputed because it's always possible to reverse cause and effect and say "he only lacks empathy because of X" rather than "he believes X due to lack of empathy".

Fair enough. It does seem like it would be difficult to tell those two things apart from the outside.

And my impression is that empathy towards only the in-group is a normal human trait and that it is often affected by society only in the trivial sense that society determines what the in-group is.

Also true (probably).

If you're trying to get the best match between map and territory though, it's worth looking for the motive for each particular evil. If you're trying to reduce evil in the above-defined sense of enjoying causing involuntary suffering, doesn't it make more sense to treat this as outgroup persecution rather than terminal "evil." I guess my point was that I don't think evil as a terminal goal exists in most people. There may be terminal goals for which evil is a hardwired strategy, but it's more important to look at what those goals actually are if you're going to try to minimize the evil. Maybe we can tweak the definition of outgroup. Maybe we can make the ingroup value something that the outgroup doesn't and then "deprive" the outgroup of that thing as our form of persecution. Just saying that "evil" exists and is a driving force feels like a mysterious answer.