As people who are in a negative mindset often need some one else who is free of a mental illness to intervene in their lives in order to help them to fix their lives and set them back on the right path.
The step would be acceptable because a person who is severely depressed cannot physically realize that life goes on. The chemicals in their brain don't process that there are other ways to feel better besides dying.
Most people that try to kill themselves don't actually want to die, as recent studies show, but feel like death is their only way out at that point. But death isn't the only way out, which is why interference is usually very helpful and of course life saving.
