I'm surprised this archaic thinking still persists. As an administrator over a multidisciplinary clinic I can attest to the validity of both chiropractic and traditional medical care.
As far as the notion of bones being out of alignment not visible on x-ray, I would agree. However when motion studies are performed, a lack of movement of one bone over another is readily evident.
Our chiropractor said that you could exercise the heck out of the area that is not moving but it still won't make it move properly. For example if your knee is fixated, you can move it and exercise it. If your L3 is not moving properly on your L4, you cannot target those specific segmental levels and incur movement with exercises (other than the wrong fixated movement). Even our PT agrees with this.
As far as cross over into other fields by chiropractors. This is actually being mandated by the insurance companies. Studies show that chiropractic adjustments in conjunction with active therapy yields the best results. Therefore it is becoming a requirement that exercises be implemented.
Our medical doctors appreciate having an additional outlet in the practice to refer to. Beyond exercise and medication, chiropractic care is considered an appropriate conservative adjunct to back, neck and extremity pain.
Even our medical doctors see the chiropractor for their ailments, due to the fact that they are unable to function when taking the pain medications they prescribe others.
There is tons of research supporting the validity of chiropractic care. However, there are good ones and bad ones as in any profession. If your chiropractor says you have to come every day for 6 months or makes you pre-pay for all your appointments, RUN! But this fortunately is the exception, not the rule.
Chiropractic education is the same as an MD education, with one exception. Chiropractors do not go through the rotations or internship like an MD. It is like starting medical school with the foreknowledge that you are going to be an orthopedic surgeon, and therefore your training is job specific.
As far as ART goes. It is a good technique, but not the only one that works.
Regarding weekend seminars. This is the case with all professions including the DO, MD, DC, DPT, DDS, or DMD. You know how your doctor knows what new medication to prescribe, the drug rep. verbally told him. All without a weekend seminar.
Hopefully this helps to clear up some of the aforementioned misconceptions.