I'm not sure, but I think psychopaths can't really be evil. Surely a psychopath is someone who commits atrocities like murder etc; without empathy- although possibly with intent, because they were born without the ability to have empathy, then they can never be called 'evil' (which I define as committing things like torture, murder, etc; with intent and as sane).
If, as many people, define it like me, that evil is with intent and also the ability to go against human emotion and empathy, then being 'born evil' is an oxymoron. If you were born without empathy for human beings, and are psychopathic, then, although doing the crimes with intent, you cannot truly understand the extent of your actions (so a sane 'evil' person would be able to understand, emphasise and know what pain the person they're doing something to is feeling, but go against it- someone with no empathy might understand it is happening but not be able to truly emphasise with the person) and cannot be considered 'evil'.
I feel all a bit mixed up about this (illness, just got back from a 14hr flight, children...). It's so hard to understand how anybody can ever do this. It's hard for me to understand how someone with agoraphobia feels for instance, I know what it is, and I can try and grasp at the feeling of having it, but I will never understand it. Evilness, or, let's just say for a moment here, lack of empathy, is hard to understand.
I can't and probably won't ever be able to imagine what a psychopath feels, how they see the world. I see the world in my way, and I see the world, like many people, with empathy.
Empathy seems inescapable- sometimes you don't realise it, but you always have it. I watch the news about Syria, and see children escaping from the fighting, and imagine what it must be like- try to imagine- and I don't even make myself emphasise or think about it, I feel sad for them, feel angry how it could happen and many other things.
I donate to charities for the homeless because when I hear about it, my mind jumps to how I think I would feel if I lost my house, was dependent on the council, was in a cramped room maybe, dealing with forms and laws and everything, trying to pay for necessities and realising I couldn't afford things which I take for granted now- washing machines, new clothes, nice food like desserts, presents for the children. Even helping someone with a pram up the steps in the train station requires empathy- a woman came up to me yesterday when I was taking the train to the airport, and said 'Sorry, I don't have children, so you might be fine, but do you need any help with that pram?' No children (although probably has experience of smalller siblings, maybe even nephews or nieces, or other children, although not necessarily) and she looked at me struggling with the pram (DH wasn't there unfortunately, and DC too young to help me) and thought 'she looks like she needs help' which is impossible to think unless you would look at me and feel sad or wonder what it would be like struggling with all of that. Although a tiny problem, empathy is still required.
So I find it hard to understand a person without empathy. I find it hard to think a sane person can be 'evil' too. I'm still not sure a sane person could ever murder anyone. Not psychopathy, nothing ever like that, but I would find it hard to murder someone. However, I've had a very nice life- I had a bad relationship with my mother as a child, and my father died- but I was never abused, hurt or anything. I wouldn't describe it as 'nice', but I was never pushed to anything close to murder. If I was abused by my mother, as quite a headstrong, quite impatient (even now unfortunately, although as an adult I've obviously controlled this!) and easily pushed person, would I have? I honestly think not- but by 'thinking' this, I'm trying to equate another, very alien, experience, with my own, which is impossible.
I think every human will see a scenario and put their own experience, life and self into that scenario. I have never experienced severe abuse (or any abuse, and I count myself incredibly lucky for that) so therefore cannot imagine the life, the feelings, the hurt, pain and emotional damage that someone who suffered it has or had- all I can do is try and picture it, but because I can't ever see it fully, I naturally will have my own life and past slip in- subconciously- which prevents me from understanding. Because I have never felt the need to murder, I can never understand a murderer. You could say only a person we consider 'evil' should be allowed to judge if someone is evil- only they have the full understanding which, fortunately I would say, no one else can really have, not a psychopath, sane non-'evil' person or other).
I think a truly evil person isn't sane, but classing it as a mental health problem is wrong too. It's something very wrong and inbetween and almost scary, but I think no one will be able to understand it unless they develop a technology which accurately sees what someone else is seeing and thinking and feeling.