Mental illness can be diagnosed from behaviour (and what constitutes ‘normal’ behaviour is indeed an interesting argument, but that’s not confined to psychiatry - it’s what keeps people in prison, for example).

You’re right that the causes of mental illness are not well understood. But it’s still possible to diagnose without a full understanding. It’s known, for example, that serotonin level has a major effect on overall happiness. While people’s ideal serotonin level will differ, making it impossible to use an objective test to diagnose this particular issue, it’s been scientifically proven (using placebo-controlled, double-blind studies with statistically-significant results) that increasing serotonin levels through antidepressants will effectively treat depression (it’s actually more complicated than simply serotonin levels, but the point still stands). So there *is* science involved, and just because it’s a step back from performing a definitive test doesn’t make it any the less valid.

So perhaps we can drop the paranoia? Like every other medical science, psychiatry is there to help people, and is built around the scientific method. It uses evidence just like anything else, and just because it’s more complicated than ‘look, this particular bit of the brain isn’t working’ doesn’t mean that it’s all a big conspiracy.

If your intent is to defend scientology, then the onus is on you to prove that your methods work. If they do, great! That means we can help more people. Incidentally, there’d be nobel prizes all round and an overhaul of medical science generally, but if it’s the truth then that’s only right and proper! However, if they don’t (and they’ve never been shown to), some critical thinking should be applied before trying to wreck people’s faith in the medical community, and their ability to live a happy life, through ignorant nonsense that somebody eloquent once made up.