I've dealt with a number of chiropractors. I go to one several times a year and have for the past decade.
There are those I respect and there are those that are scam artists. The ones I respect are the ones that know the limits of their practice. The ones that are scam artists often use x-rays and neck angle to dupe people into "treatment" they don't need, using words like "natural healing power" and "life force".
The over-arching problem is twofold.
First, like many alternative treatments, there is very little real scientific research backing up their methods. Within chiropractics, they do studies, but they typically fail to meet scientific rigor in a number of areas, including controlling for bias and methodology.
Second, and much more worrisome, is that chiropractors are not medical doctors and are rarely trained to properly refer people when a problem is outside their area of expertise. I've seen this with both of my parents. My mother had knee pain, which the chiropractor (which was one of the ones I respected) insisted was an alignment issue. In reality, she needed a whole knee replacement, and suffered unnecessarily for a number of months before seeing an orthopod, because the chiropractor insisted he could fix it.
My father had severe shoulder pain, extending all the way down to his fingers, and eventually started losing functionality in that hand. Again, the chiropractor thought he could fix it. My father had a severely herniated disk which was impinging a nerve. Again, he suffered unnecessarily because chiropractors do not refer people when they're out of their element. Finally, a neurologist determined that surgery was the only way to fix the problem, which it did. He has regained 95% of the function of his hand.
I think chiropractors have their place and can help with some skeletal alignment issues, but there are significant problems with the industry as well, and people should be aware of them before going in.