This subject came up before and Albea gave her comments
and also a link to an article by Andrew Vachss that goes right
to the heart of the problem with abuse of children or animals.
This article distinguishes the differences between sickness and
evil. (Sickness is a condition.Evil is a behavior). The article is at;

http://www.vachss.com/av_dispatches/parade_071402.html

Society can change (really must make changes) to insure our
survival as a species.