I think they can have their place, just like any practicitioner. But there are a lot out there who are nothing more than crack dealers - Since the crack feels so good immediately after but the effects wear off so quickly. My husband has serious back injuries (triple fusion, five herniated discs, spinal cord damage) and has been to many chiros over the years. Only one was genuinely good, promised only temporary relief and wouldn't touch him without evaluating his MRI's and x-rays.
I've been to chiros over the years as well for accute issues, sometimes with success and other times without. Probably the most noticable was during my first pregnancy when I had horrible carple tunnel due to swelling. The chiro manipulated by elbows and wrists over three visits such that the pain went away completely. The numbness was still there until after the baby's birth but getting rid of the pain was heaven. The MD had just told me to deal with it.