> Rather, it's a byproduct of a seriously messed up world/society/personal relations landscape, that depressed individuals are more sensitive to or have felt more deeply.

- Even if this were true, that doesn't preclude depression from causing biochemical changes (e.g. inflammation).

- Saying this is the only cause of depression doesn't make a lot of sense because it doesn't account for, say, post-surgical or post-viral depression.