However difficult it may be to contemplate the reasons for Breivik's killing spree does not excuse trying to reduce the reasons for his behaviour to a brain abnormality damaging his so-called affective empathy. (Autism is said by Baron-Cohen to be an abnormality of cognitive, rather than affective, empathy.)
This illustrates the problem of a biomedical understanding of mental illness. War (which is regarded as a sane action) is justified on the basis of "goodness not evil" in the same way as Breivik has justified his behaviour. Breivik himself compared his sacrifice of 77 people to the dropping of the atom bomb on Japan, preventing more deaths in a civil war which he believes will arise out of multiculturalism. His reasons couldn't be any clearer - speculating about his brain abnormality is a distraction.