To me, clinical depression is a real illness that is belittled by people who think that bad patches are a symptom of them being depressed.
Although I don't personally think I would ever contemplate suicide, I've never been clinically depressed so I guess it's quite difficult to understand why anybody would want to cut short their life.
I don't personally have a strong stance on euthanasia, because, like abortion, I don't really think you can understand the situations of individuals who are faced with the issues unless you're in their shoes.