This is a great question. The simple fact is this; Chiropractors receive almost the same amount of training in their 1st 4 years as medical doctors do and even more training in their expertise, the spine and nervous system.
The major Chiropractic schools are all overseen by the Federal government and all Chiropractic students must pass rigorous National and State Board Examinations.
By the time a person becomes a Chiropractor they are as highly trained as a general medical practitioner and even better trained in the maladies of the spine and nervous system.
In fact, Chiropractors have more training in nutrition, the spine, the nervous system and the skeletal system than many MDs.