There is a principle in science called the law of parsimony. The law essentially states that if there are competing hypotheses to explain a phenomenon, the one that has the fewest new assumptions should be the presumptive hypothesis. The common reduction of this law is that the simplest explanation for a phenomenon is likely the correct explanation.
In the mental health field, we have had reasonable explanations for depression and anxiety for millenia. The explanations we have had have been perfectly adequate. Biological, economic, social, cognitive, and other causes are plentiful and more than enough to comprehend depression and anxiety. We do not need additional explanations, any more than we need another explanation for why it appears that the sun goes around the earth (the heliocentric explanation).
If you begin with the presupposition that depression is a normal response to the often overwhelming experiences and choices of life, then you can presume that the causes of depression are intelligible and discoverable. Then they can be comprehended and controlled.
If you begin with the presupposition that depression is a disease, you will not feel compelled to search as diligently for humanistic/existential/relational causes. This is ultimately dehumanizing. Therefore, psychiatry is dehumanizing.
We do not require a medical or even a scientific answer to why people become depressed.
Common sense is sufficient. Common sense is more than sufficient. Common sense, therefore, is where we should look when dealing with depression and anxiety. The answers aren't in a SPECT scan or the synaptic cleft; they are in LIFE and our HUMANNESS.