As a parent of a develpmentally disabled person, I’ll agree to your statment about victims vs perpetrators. I’ll point out though, that we here are not doctors, and not making diagnoses. And we are not in a court of law making judgements of fact. We are an ostensibly public forum, voicing opinions.
For the audience here, I’ll venture that “All persons with mental illness are not dangerously violent.”, is a given? If you want people to agree to the (presumed? demanded?) corrolary of, “All violently dangerous people are not mentally ill.”, then I think you have to give us some other language than, “Stalin/Hitler/Manson/and this latest %*/!& with an AR-15 are assholes.”, with which to wrap our brains around the horror.