h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

"Evil is really terrible human behaviour. It's based on greed, and fear, and hostility, and all the other bad human traits."

Yes - this is similar to how it is often suggested that the perpetrator of an atrocious act must be mentally ill, which is a way of avoiding the concept that an atrocity has been committed by a human who planned the atrocious act for a reason. This does a disservice (to say the least) to people living with mental health problems...

I agree with you, Sasha.

Also, mentally ill people can make good or bad decisions, the same as anyone else. Depending on the kind of illness they're dealing with, their ability to make those decisions may be impaired.

I think a lot of confusion arises from a misunderstanding of the McNaughton Rule:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2902100/

If a person killed another person while convinced that person was an alien from another planet trying to kill *him*, that's a delusion, but the decision was made to act in self-defence. Think about John Forbes Nash - he behaved in what he thought was an honourable fashion. He just had the wrong facts.

If a person is deluded in thinking that perfect strangers are souring his lifestyle, and kills them out of animus toward that group, that's still murder, no matter how rational or irrational you feel his prejudice is.