In this piece about him in the Independent Simon Baron-Cohen is quoted as saying that...
... the term evil is unscientific and unhelpful. "Sometimes the term evil is used as a way to stop an inquiry," Baron-Cohen tells me. "'This person did it because they're evil' – as if that were an explanation."
Sometimes the term 'evil' is used to block off further explanation. Nonetheless, even if the concept of evil had no explanatory value - something I'll simply accept for the purpose of keeping this post short - and even if evil is not a scientific concept, this doesn't prove that it's a dispensable or an unhelpful concept. It might fulfil a useful classificatory function. I will propose four reasons for thinking that it does.
First, there are acts that are bad or wrong and which it seems inadequate to call merely bad or wrong. We want a term to capture their extremity - of cruelty, viciousness, etc - and the horror they widely induce, in a way that our ordinary terms of moral disapprobation don't. 'Evil' seems to fit the bill.
Second, although Baron-Cohen's thinking is framed in terms of the biological determinants of actions which show a lack of empathy, if there are still meaningful human choices, then it is possible to regard some of these, and the acts that follow from them, as not just misjudged or wrong-headed but as morally depraved in the degree of their inhumanity.
Third, as acts, so also policies, institutions, regimes. If these centre closely on, if they require or encourage, a multitude of inhuman(e) acts, then it seems apt to describe them with a sufficiently condemnatory word, such as 'evil' is.
Fourth, people can be thought to be evil. Not everyone who is guilty of what we call an evil act, and maybe no one who is, need be unchangeably evil. But those who persist in acts of the relevant kind, when they could do otherwise, may reasonably be thought evil until further notice.
The real difficulty - one I won't go into here and to which I'm not sure of the solution - is how precisely to delineate the concept of evil. What are its defining components? That's a big philosophical question.