Lung cancer and most other physical ailments have legitimate, objective diagnostic criteria. You get a test or two and find out if you have a specific disease. I.e., science.

Psychiatry, except in rare cases, does nothing of the sort. Most discussion about mental illness (including your post) is an attempt to induce people to apply fallacious reasoning about it - you've developed intuitions about cancer, now go incorrectly apply that intuition to depression/drug addiction/etc.

http://lesswrong.com/lw/2as/diseased_thinking_dissolving_que...

If you wish to argue that a given animal can fly, "penguins fly just like crows fly, they are both birds" is a fallacious argument. Similarly, "do X for mind disease just like you'd do X for lung disease" is a fallacious argument.