How can you assume that people critical of chiropractors haven't ever used one? I've seen a few over the course of my life and one of them did relieve pain to an extent. I've since found out my back is in worse shape than before visiting the chiro, even though he helped relieve the pain. I also had a tumour in my leg for which I saw a chiro for treatment after surgeries. He fscked things up so badly that I had to have my bone-graft reset.
It's not about whether they relieve pain, which they can under acute circumstances. It's about the collateral damage associated with the process. It's like being offered a pill that might relieve some pain but at the cost of it potentially killing you at any moment or causing you to become paralysed. That kind of treatment for pain would never see the light of day from approval bodies, yet because this is a service and not a pill, it is somehow measured by a different standard, by regulating bodies and clients alike.
Just take a look at the list of victims already posted here. The dangers are inherent, they're not based on malpractice. The entire process is malpractice to begin with. Look at the con-man techniques used by them - faith healers use the same tactics to prove that they can make someone's legs grow. Look at the ridiculous notion of them taking x-rays for things like pinched nerves. Look at their process of evaluation, which is nothing short of assumptions lumped on top of each other. Then look at what it is they can actually help with - vague, undiagnosed pain. Then realise that they have no qualifications for diagnosis, nor actual medical backgrounds to be able to evaluate the risks of what they do.
These charlatans can't diagnose, nor treat anyone who has a real, physical manifestation of actual diseases, cancers, syndromes, real spinal injuries, traumas etc. They're glorified massage therapists who use an additional technique to manipulate the bones and joints in your body - they do this based on an antiquated principle that all of the body's ailments stem from the spine. We now know this not to be true, but they continue with the practice.
Just look at how they market themselves to people with arthritis and headaches for example - they should never, ever be treating those people because the risk factors there are stroke, death, and paralysis. Real risks with real world victims. They do not warn you of this beforehand. They unethically market themselves as a viable treatment for these ailments, and they do so irresponsibly. That's not the sign of an upstanding profession.
TL;DR - Yes, it can relieve pain, and only some pain, but at what cost?