I believe it should be their choice to make. The case in which I'd be skeptical is if someone were just beginning to experience mental illness. The onset of mental illness can be very difficult, confusing and disturbing. People often don't know what's happening to them and they don't know what treatment may be able to do for them. To allow them to choose suicide in an dark early moment of their disease which may stabilize seems callus to me.

I'm not sure how you structure this limitation but bottom line is anyone with significant experience of their own mental illness who doesn't want to live with it anymore shouldn't have to.

The whole point is that they are unable to make that choice. A substantial decision made in sound mind implies rationality, which mental disease, by definition, diminishes.

If you equate a person's rational choices with everything that comes out of their mouth, then you will euthanize a whole lot of mentally troubled or people.

Just because someone is experiencing mental illness doesn't mean they are irrational.

I'm not even sure it's possible to divide the world between "mentally ill" and "mentally well". And if you could, I'd be inclined to say almost anyone who has been in serious chronic pain for years cannot possibly be considered "mentally well". Pain takes its own toll.

Depression absolutely makes people irrational. It changes your risk calculus. Are we going to act like other disorders such as bipolar are rational and should be listened to whenever at face value?

It can make you irrational. It doesn't necessarily. You are acting as if all mental illness is experienced uniformly the same across all people. It is not. And as if the severity does not vary over time. It does.

And dependimg the disease condition of the bipolar suferrer yes. Depending upon their stability which varies heavily from case to case and individual to individual. Would you want to do so at the peak of mania or the trough of depression, probably not.