What is wrong with this headline?
Only someone with a mental illness would be labeled this way. He isn't considered a person - he's one of those scary crazy guys who did something horrifying to someone else, and so this is what he's called. I guess "Person with schizophrenia admits knife death" isn't as sexy.
If the man had diabetes, the headline would not read "Diabetic admits knife death."
If the man had luekemia, the headline would not read "Luekemic admits knife death."
But since the man has been diagnosed with schizophrenia, this is what we get.