I'm not sure I follow? If you rule out any other motive, someone stabbing someone else in broad daylight, unprovoked may be attributed to mental health issues.
But everyone has mental health. If you have a mind, then it's in some form of health. An extremely broad, arguably meaningless, classification. All it does in this context is reinforce the public stigma towards the millions of perfectly good people in the community dealing with hugely diverse situations from depression to autism and far beyond.