The basic question is whether the one doing evil perceives himself/herself as such. The challenge is that there is a great difference in how to relate to one who, on some level, recognizes his/her actions as evil and one who does not -- even perceiving them as, in fact, good. I expressed my thoughts further on this in my latest Huffington Post blog: The Problem With Deeming Someone "Evil"
original title for the post, btw, was 'Determining Good and Evil' but it
was changed by the editors. (I leave it to you to decide which title is better.)
feel free to comment here or there.
Rabbi Ben Hecht