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.
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.