It is when it is the only medical care these people can afford.
Except at least in the McDonald's case you have to eat food to survive, so you may not have a choice. You don't have to go to a chiropractor to survive, so it's better to not go there at all than it is to go and receive possibly dangerous treatment from a con artist.
Remember, there is no science behind what they do. They don't know if they're going to hurt or paralyze you because they never went to medical school!!