Just as I would not go to an internist or GP for trauma force relief of my joints...I would not go to a chiropractor for internal medicine or yearly checkups...and yes be very careful...because good doctors are rare...do not be a sheep...use your brain and research what your doctor is telling you...and make sure they are right...after all if he is wrong you are the one who is both responsible and vulnerable...
Blaming this doctor is misguided anger, perhaps you should be blaming yourself for not insisting that your father be checked out on a regular basis...your chiropractor telling your dad he was healthy is not negligent...as far as his joints and nervous system he probably was...