Yes, quite often they are. That is what I'm telling you. People can do terrible things and not be mentally unstable or even very different from you or I. All they need is a reason. What we see in a lot of these situations is that the person was convinced that what they were doing was justified. That they were the good guys. The only reason you see them as mentally ill is because you disagree with them.
Yes, but what made them the kind of people who would think what they were doing was justified, were their experiences. And how is that radically different from someone who is mentally ill because their experiences made them so? I'm just not 100% convinced there's a very clear line between the two. People's experiences determine their character, but sometimes we decide that what they have become constitutes mental-illness and sometimes we decide it's just a moral issue or character flaw, and I'm not sure we really know which is which.
I have similar doubts about less morally-charged things like ADD or dyslexia or 'oppositional defiant disorder' (a new one to me, which sounds like just a clincal-sounding term for 'bolshy'). I'm not making a sneering point that 'dyslexics are just thick', rather it's that I'm not sure that someone who just has trouble learning to read but isn't classed as dyslexic should be blamed or disparaged any more than someone who has a diagnosis.
Some people with certain problems and behaviours get defined as having a 'medical condition' while others don't and just get morally-judged instead - when probably everyone who has issues has an reason for being the way they are.
I'm being a bit abstract and wandering off into philosophical concerns, but it's unsettling that we can blame someone for being who they are, right up to the point where it gets a diagnostic label, then suddenly we are supposed to be more understanding.