In addition, certain psychiatric conditions can be acquired or unmasked under extreme stress. Shall we put everyone going through a divorce or a serious illness of a loved one on leave?
I can't think of the last time something like this happened, but these events are very rare.
This is a valid point and maybe we should be re-assessing not mental illness but that way we perceive mental illness.
You note divorce and the serious illness of a spouse. Where I fly those two exact scenarios will get you time off with full pay. During that time, you will be assessed with regard to your fitness to fly. It is hard to explain, but the extreme discipline of flying sometines can be a necessary break. So often a reduced schedule is "prescribed" with the option not to fly at all.
If companies, (not just airlines) viewed mental illness the same way heart disease or cancer was seen, then maybe that stigma would be erased. Either temporary or chronic mental illness should allow any employee the option to take time off to get one's gyros re-aligned, if possible.
As to the rarity of the event. I can't remember any occasion where an employee "stole" a transport aircraft and took it for a test drive.
Just because I stopped arguing, doesn't mean I think you are right. It just means I gave up!