That portion of the article is referring to clinical depression, not general loneliness and unhappiness. You just demonstrated his point (that people have a hard time seeing mental conditions like bipolar disorders as actual diseases of the mind and not just bad attitudes) quite nicely.

Pardon me for being frank, but when I pause to imagine having my life taken from me before I was done living it, or being so profoundly unhappy that I would sincerely attempt to kill myself, I can only see both as terrible in their own right. There's no sense in trying to compare the severity of one to the other.