I see where you're coming from, and I don't disagree that there is plenty of research to be done here: differentiating different types of depression and anxiety

I see where you're coming from, and I don't disagree that there is plenty of research to be done here: differentiating different types of depression and anxiety, detailed fMRI studies, getting more knowledge about chemical imbalances and how the drugs operate etc. But mood disorders aren't in the same ballpark as physical ailments. I mean, even a common infection can be impossible to diagnose unambiguously from a simple blood test, and mood disorders usually interact with who you are as a person. You can't just make a machine that solves this. I doubt you're the kind of person to be convinced by an anecdote, but I suffered recurring depression and anxiety for a period of five years and was almost completely cured by a combination of SSRIs and CBT. What seemed to make me get these recurring depressive episodes was a combination of unhealthy thought patterns and behaviors. Holding myself to impossibly high standards, having a habit of disregarding my accomplishments, working very hard with no long breaks, being overly critical in social settings and a lot of other small things that were very much part of my personality (and incidentally, very common in the tech community). No one would have classified these behaviors as excessively weird or pathological, but they turned out manifest in long-lasting and serious depressive symptoms. The question is, how are you going to measure behaviors and thought patterns like this with a machine or a physical measurement? Maybe you could just say that "okay, so the depression or anxiety isn't a symptom of something that's wrong, it's a problem in itself, which we could somehow fix physically or chemically". But then you're moving into some pretty dodgy philosophical territory. Mood disorders simply can't be a hard science with the degree of understanding we can hope to get in the near future. And although there's plenty of research to be done, the methods we use are pretty good.