I agree that I would not trust most chiropractors. The nature of spine adjustment is and has to be regarded as a very specialized field. As you are correct, it could lead to many an issue anywhere from the neck down.
I have been to a chiropractor numerous times on my journey. While I agree that there are numerous ones that I would not trust to adjust my pinky let alone anything else. There are a few that are very reputable, caring and knowledgeable on what they do. In fact I would trust my chiropractor more than some of the spine doctors I saw. I had some MDs wanting to do lumbar fusion to "treat" my condition.
I did have a cervical fusion some 15 years ago, successfully, and my chiropractor will not adjust anywhere around that area, rather he will massage to loosen up or adjust.
So I would say there are bad apples in all fields, just do your research and if you don't have a warm and fuzzy feeling leave. Even if you already paid a copay, leave if it doesn't feel right. That little amount of money for a copay will never equal the pain and suffering a bad dr will cause.