If you believe in life after death (redux) ....

It's relevant to the fact that you're claiming that a mentally ill person's request to die doesn't reflect their actual feelings, regardless of how many times they repeat it with conviction. And you've just ignored the question about whither this 'value' derives that you wish to conserve. "Don't harm, especially the mentally ill" leaves the person vulnerable to the harm that they want to escape and only 'harms' them from the perspective of those who will not be the ones receiving the treatment. There's no justification why the 'harm' as others perceive it should be considered more important than the harm that the patient is actually enduring and will continue to endure.