I dont disagree wirh you, and terminal illness is certainly one of the rare situations where a such a decision might be considered rational.

I was referring primarily to individuals suffering from mental illness where the issue is more lack of treatment than lack of possibility of improvement. Many feel their decision is perfectly rational because their minds are not functioning correctly and they are incapable of making a rational decision at that moment.

You're not endangering my worldview; I am sorry that you're facing a terminal illness and I hope that you're able to find something to extend your life as much as practical and make as many of your remaining days enjoyable as possible.

I don't say this out of some religious fervour, but because the future is always frustratingly unknowable, and there is always a chance that today's insurmountable hurdles are tomorrow's speed bumps.