Either you can kill someone without having to have mental health issues (even though a soldier killing an enemy is accepted, it?s still killing, but they?re not deemed as having mental health issues), or we all have mental health issues. Anger can be quite a powerful motivating factor for killing someone, without having to put a label of ?schizophrenia? or something on it. Perhaps there?s no mental illness at all, since the criteria for a certain disorder can always change. There?s just a ?mental health spectrum?, and some people are further down one end than most others.
Also, very few people know what psychopathy/sociopathy actually entails. I know a lot of people who come across as selfish and uncaring of other people?s feelings, but I wouldn?t call them a sociopath. I have a sort-of-but-not-really friend who laughs at videos he finds online of people getting beheaded (mostly Islamist soldiers, but still), but he?s not a sociopath. He?s just a dick.
Aside from murder, what about rapists and human traffickers? Are they mentally ill, or just bastards? How about Elliot Rodger ? a young man with the world?s worst ?Nice Guy? complex? frustrated with how shit he perceived his life to be, or a textbook example of someone suffering from narcissistic personality disorder and supported by having been in long-term therapy? What about child molesters? And that includes the regretful ones, who claim to have been sexually addicted rather than wanting to cause actual harm, and even a lot of non-paedophiles in society don?t really treat children as people ? not until they become adults, at least.
But none of us are real psychologists anyway.