What is true is already so.
Owning up to it doesn't make it worse.
Not being open about it doesn't make it go away.
And because it's true, it is what is there to be interacted with.
Anything untrue isn't there to be lived.
People can stand what is true,
for they are already enduring it.
—Eugene Gendlin
(Hat tip to Stephen Omohundro.)
It looks like there's still some serious controversy on the issue.
But suppose for a moment that it's true: Suppose that depressed people really do have more accurate beliefs, and that this really is related to their depression.
What does this mean for rationality? Is it more rational to be delusional and happy or to be accurate and sad? Or can we show that even in light of this data there is a third option, to actually be accurate and happy?
If you're an egoist, it's best to be delusional and happy. If you're not, the needs of others outweigh your own. Of course, even if depressed people are more accurate, that doesn't mean that they're more productive. Then again, they may be able to use their more accurate beliefs to find a better charity and make up the difference. Of course, you could just have a depressed philanthropist tell you where to donate.