For the record, I think that this thread kind of illustrates the stigma that people with mental illness, disorders and disabilities have to deal with - this idea that they're choosing their behavior as much as those without it are, or at least enough to be held responsible for it. I think what a lot of people don't get about mental illnesses, et al. is that it can, oftentimes, have just as significant an impact, if not more, on "choice" as physical illnesses.
A person with Parkinson's disease cannot stop his body from moving and nobody would dare chastise him for knocking a glass over at dinner. Imagine having that same kind of lack of control in your mind - the one place where you're supposed to be able to have total control - and then being told by others that that lack of control doesn't exist and that your behavior is all your fault. That attitude is a problem. I'm not saying that nobody with a mental illness, disorder or disability can control how they express what their brain is making them feel or think. Many people can control it, but some cannot and even those who can often have significant barriers to doing so - more than those without such problems.
Moreover, just because we might stop caring about the causes and explanations for murder and similarly violent acts doesn't mean that those causes and explanations actually go away. It just means that we're ignoring something because we feel like it.