Just because we can understand their reasoning and why they do things doesn't mean that We have chosen to do the things that they do. It is the choosing to do that makes one evil. It is my belief that the twisted nature that most evil people have is not uncommon. What makes someone evil is that they choose to follow that darker side and do the things we hold despicable.
It is not understanding or even being temped to do certain things that makes one evil. It is the doing of evil things that makes one evil.
I've never heard about that that somebody called Dostoyevsky an evil person due to the fact that he get into Raskolnikov's psyche in "Crime and Punishment", so in my opinion such statement isn't right.
Thinking of evil, and understanding evil, does not lead to evil actions.
Greatest example: There is a unit in the FBI that studies human behavior. They get into the minds of criminals every day, and think like serial killers and murders. They are police trying to save lives, yet they think like evil men.
I get psyched for all of my characters. The thing is is that a good story must have two sides the good and the bad but they are only good and bad in one perspective. Also people aren't born evil (unless this is children's books we're talking about) I love to write about an evil character's background. An example of one of them is in a story that I haven't yet posted yet. The antagonist in that story traps tortures and kills a lot of my characters but he is my favorite because of the reason behind it is so terrible and sad I just can't help but to feel bad for him (and also because he is going to change his ways). I hope this makes you feel less evil when you fall in love with the most despicable characters
Fair enough. but how do you reconcile the fact that most people believe that "thought is action" for example if a teacher looks at one of his students and tells a friend that he's dreamed about her... he gets fired if the staff of the school find out. He hasn't actually DONE anything wrong, merely thought about it but he is fired for that thought. So society is enforcing the idea that "thought is action"
By extending that to its logical conclusion, then such thoughts as are mentioned in the question are surely indicative of the person being evil no?
I really don't understand this "thought is action" argument and the story of the teacher getting fired over something as incontrollable as a sexual dream sounds very unlikely to me. I have never met a person who believes in "thought is action" and I doubt that most people do.
In order to create a character with an interesting personality, I believe a writer has to somewhat get "into the psyche" of the character. This is also necessary for darker characters and darker actions. Normally a good story needs a villain of some sort and villains need to do some evil things in order to be a believable threat. If the protagonist is the one doing the evil action, his/her character also gets a bit more depth.
But does this make the writer evil? If a writer writes about a little boy who wants to have a tricycle for his 6th birthday, does that mean the writer wants a tricycle? Of course not. The same can be applied to the serial killer character. Writing about a serial killer doesn't make the writer evil. In fact most violent stories to some extent at least function as a monument of the terror it describes, to keep people from commiting "evil actions".
Good and evil is only from the view point of a society. For the answer to your question, in the view point of our society, the answer is still a very difficult one to answer. More than likely it would be no. It's alright to think a way, as long as you are not doing it. However, some people think that if you begin to think a way, you become that way. This I disagree with, for it holds little and fragile logical grounds.