Evil

Situational evil is when a normal every day person is subjected to a hearse environment. This can happen to anybody and most of the time it occurs with the best people. this happens because people want to have power then they show it by making others do acts that they would never do. This type of "evil" if you can call it that is not preventable  because some people are power hungry. that is just something you cant change.
In the movie there was a very controversial baptism that took place on a serial killer. He believes that religion can remove evil form the person. One baptism can not make what that man did go away. He murdered about 11 people and cut them up. 
In the brain there are normal responses for a hard choice that flag up as no. If the need is dire enough you can over power the normal response. That is not evil. Sometimes one death is the best for the group.
Orders are not exactly evil it just depend on the way that they are told and brought to completion. The thing about orders that is evil is when you do something you were not told to do like reaping mothers and daughters in front of parents and spouses.