Just to balance, I have been going since mid 04 {for a chronic condition}- I hope he never retires.
I really think skill and technique has a lot to do with it.
The DC I go to is very gentle and precise in his adjustments, not rough or forceful at all.

If you go to one that just grabs and yanks you around !
I do agree that there are bad ones out there.

It is very important to check them out first as much as you can before you allow any hands on.
They should request x-rays before even doing any adjustments to check for possible problems.

In the Google & You Tube videos there are quite a few videos that show a variety of chiros and adjustments being done. Most that I have looked at so far were good and gentle and precise.