Could you explain how you don't think mental health therapy is a science? We have psychology as a major in most universities, unlike chiropractic studies which are usually offered in different or specialized institutions. We have doctors of psychiatry that are actual doctors that can prescribe medications, just like general practice doctors. Therapy in different fields, whether it is in individual mental health or couple's therapy are active areas of research in academia with published works you can read up on. So I'm not sure how you're equating Mental health with Chiropractic practice.

It isn't a placebo effect, as you mentioned. Therapy isn't a cure/medication like drugs or a surgery for some diseases, therapy is more akin to exercising your mind so that you can face stress/fears/ any kind of emotional turbulence without losing it. Or as an avenue for personal growth or reducing effects of mental trauma. Saying it's a placebo effect without backing it up could be actively harmful for people who might be considering it and actually need it. Yes, it's not for everyone, and every therapists is different and every patient may or may not be willing to put in the work for it, but that doesn't make it ineffective or a placebo effect. But how is that different from, say, how the covid vaccine affects one person vs the other (some experience more protection and/or suffer from mild symptoms for a couple of days, etc.) or how chemotherapy may work for some patients but not for others?

First of all, I agree that it would be great if a drug/medicinal procedure would cure a certain condition in each and every patient or at least the vast majority of them. Sadly, that is rarely the case, but that by no means is equivalent to say that when this drug or procedure helps, it's mostly or entirely due to the placebo effect. That's the whole reason we need randomised controlled trials as their might be a significant difference in treatments that only becomes clearly observable once a certain sample size is reached and possible confounding variables are controlled for (usually by randomisation). The human body and many of diseases are incredibly complex so it's naive to assume we could forsee each and every possible influence on a drugs efficacy and therefore determine without error how a patient will react to it.

While there is quite a big group of non-responders when it comes to psychotherapy, it is, on average, an effective treatment clearly proven by a vast body of research. There is still much more to find out, but putting it on the same level as not consuming gluten is in no way defensible.

Now to get back to chiropractics, I don't know too much about it, but I thought it's mostly short term pressure and pain relief, which however rarely combats the underlying issues. Can still be helpful, of course, as pain relief helps with getting more physical activity, as this is often a culprit for example back problems.

That said, I personally wouldn't let anyone touch my spine or neck like some chiropractors do. I'd be too scared of irreparable nerve damage.