If a remediable cause can be found (for example, depression and society's attitude towards it), the problem can go away.
And the problem is far from microscopic; not all murder-suicides are flashy: http://en.wikipedia.org/wiki/Murder%E2%80%93suicide
However when you consider how unexpectedly schizophrenia can creep up on people, or how unexpectedly PTSD symptoms can go from mild to severe (just two examples) even with significantly improved treatment we'd still have it happening now and then.
And even if it happened only 10% as often, it would still represent a minuscule risk for most people, perhaps slightly closer to lethal asteroid impact than to lethal food poisoning from Sushi on the risk scale.