If you'd look you'd find plenty of evidence of the sort that you think doesn't exist. Try a popular book like Against Depression as a starter. I think that the existence of such evidence also invalidates the rest of your prejudices that you express.
I don't have time to read every book out there, so when I look for answers to questions like this I look for sources that are authoritative, that is, sources that summarize the majority opinion in a field. The book you recommend doesn't seem to be that, and so I'm not convinced that it's worth reading. Are there particular studies in the book that specifically address whether depression is qualitatively different from unhappiness? Does the book cite mainstream opinions by psychiatrists and if so, what opinions does it cite?
This is not secret information, some key google terms may be "biology of depression" or something like that.
Just one piece of the literature that you might find convincing (not sure if its from that book or another) that you might find convincing is that there are structural differences in the pre-frontal cortex that can be seen under a microscope. The biological basis of depression is something that's so well established that strident doubt of it means that you can't be troubled to look for anything. It's like being convinced that evolution can't possibly be true because biologists can't be trusted.
I think that a "biological basis" means something different to you than to me. How exactly do these studies show that depression is different from being unhappy? Did they study the brains of merely unhappy people and find no such biological differences? Again, in my understanding psychiatrists and researchers make no attempt to differentiate between depression and unhappiness because they have no reason to make this distinction.
I'm going to assume that your argument is that if depression is caused by biological factors then it must be treated differently from unhappiness that is caused by life events. But in that case you will have to explain how this is consistent with the fact that "...depressive episodes are strongly correlated with adverse events..."[0]. This fact seems more consistent with either reverse causation (depression causes biological changes) or that depression can have multiple causes, and can occur in the absence of a biological cause.
