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.