"In summary, compared to nondepressed indi- viduals, depressives are “nay-sayers”. Depressives may be sadder but they are not wiser; rather, so- called “depressive realism” results from the bias of depressives to say “no”"
Cell division is obviously important for organisms to function, but it can run amok - that's cancer. Similarly, pessimism is sometimes a useful approach to solving a problem, but it becomes debilitating when it's out of control.
Depression is not a "problem solving mode" or anything like that; it's a disease. Depression (the medical condition, not just pessimism or being sad sometimes) is totally and completely draining. Someone who is depressed does not have the energy to solve the problem of "should I take a shower today," let alone "hunker down and deal with hard problems."
Sorry to pick on you, I just find the comment threads on articles like this so frustratingly ignorant sometimes.