> You don't need psychology to recognise symptoms. Unless you're saying psychology has it's own set of symptoms and it's own terminology - which is just a truism.

Psychology precisely defines syndromes (clusters of symptoms), and then, in terms of syndromes, provides both:

• tests qualifying patients into those syndromes (usually in the form of various rating scales)

• specific flowcharts for known-effective treatments for patients qualified into a given syndrome

It's not the rigor of physics, but rather the rigor of engineering or civic planning: making rules for doctors to follow that have been found in clinical practice to optimize for population-wide outcomes.

> How could you claim that the 'underlying pathology is benign' without even knowing what it is?

Because we have figured out what the underlying pathology is in many (not the majority, but many) cases, and almost every underlying pathology we've discovered is something benign: e.g. a genetic mutation that causes your synapses to produce less of some messenger-chemical. Such mutations have no long-term effect on your health, other than affecting your psychology. (And most of the cases we don’t understand present the same, are treated the same, and have the same long-term health outcomes if treated or ignored, and so are very likely to be similar in etiology to known diseases, despite not having yet been specifically researched.)

Also, as I said, psychiatrists pre-screen for non-benign pathologies first, often too widely. You can't get diagnosed with clinical depression (by a psychiatrist who's doing their job) until you've been checked for vitamin deficiencies, hypothyroidism, anemia, diabetes, etc. Even in cases where you have 100% of the symptoms of clinical depression, including ones that have no organic basis. They'll still do the pre-screen, just to be sure you don’t have clinical depression and one of those things.

But once you're known to not have any of the known-malignant pathologies, then they can and will treat the symptoms, because at that point the only problem they have left to treat is the symptoms. (What else would you expect them to do? Drill a hole in your skull to biopsy your brain tissue, to figure out what step in amine metabolism is failing—just to end up with the same treatment they’d get to from looking at the symptoms?)

> Except you really have no idea how many 'psychological diseases' could be progressing and/or affecting you

There is the simple observation that these syndromes aren't degenerative. People can have e.g. untreated ADHD all their lives, and they won't live less long or end up in the hospital more often than people without ADHD. That’s despite ADHD being a syndrome with potentially dozens of etiologies. Everything that causes that cluster of symptoms, and only that cluster of symptoms, is equally non-degenerative, because it’s all equally being expressed solely as the same kind of non-long-term-harmful down-line effect.

A degenerative neurological disease makes itself pretty obvious. Neurosyphilis is easy to recognize the symptoms of, to the point that even doctors in the 1700s could make the correlation that patients with that set of symptoms at age 60, were the same people having a lot of casual sex at age 20.

> while you mask the symptoms

When we treat a syndrome, what we're treating for usually is our best understanding of the etiology. Sometimes we're "sawing off one leg to make it even with the other" (e.g. you have too few dopamine receptors, so instead of telling your brain to make more — which we don't know how to do — we tell your brain to make less dopamine), but the treatment chosen is still putting the upstream system into a new (and beneficial!) equilibrium state, rather than “masking” down-line symptoms in the way that e.g. painkillers do.

(Though I would note that even painkillers are therapeutic in some cases — as often pain itself can have negative short- or long-term consequences, e.g. acute inflammation or acute increase in blood pressure in response to the pain. A non-negligible part of the reason that people are given opioids when they’re in severe pain, is to decrease the risk of them having a heart attack or going into shock.)