I too swear by most of them. My parents first took me to one when I was 6 months old and my legs were starting to turn pigeon toed. He adjusted me on his lap.
I had a bad experience with one when I was older and didn't go again for years then I went off and on every couple months now recently started going in the beginning of January and feel so much better. I think they are just like any other medical professional. They can hurt you and they can help you.
I was sitting in the office a few weeks ago and heard the dr telling a patient (very small office) he was telling how this big guy came to him (over 6 feet and over 250 pounds) had severe pain in his back. As soon as he started working on him he could feel his muscles making a popping sound without even adjusting him yet. He asked the patient do you drink much water and he said No - couldn't remember the last time he drank a glass of water. He asked how much pop do you drink? Oh about 6-8 cans of moutain dew or pepsi a day. Dr said to him your muscles are dehydrated and that is the cause of your back pain they are causing them to stick together instead of sliding over each other like they are supposed to. Decrease the amount of pop and increase your water and your pain will lessen - soon the patient had given up pop and drank only water and he pain had been cut in more then half!