My anti-dentist-ness started at age 16. I needed a wisdom tooth removed (just one; it was coming in wrong). The dentist wouldn't believe me that the novacaine wasn't working (I'm pretty much immune to it), and turned off the gas because I was inhaling too much... in my panic and pain! Things got worse: my tooth broke as he was removing it (I've since learned that my molars have curved roots, so they're tough to remove without damaging jawbone and breaking off root bits), so he had to basically hammer it out using this medieval torture device with a weight and spring-loaded chisel end. He knelt on my chest and held my head down with one hand while bashing away at my jaw with the other. The nurse kept my hands down. The pain meds didn't work. At least an hour went by. FUCKING NIGHTMARE. I still get all tense and sweaty thinking about it. That was, what, two decades ago? Remember that scene in "Alias" where Sidney gets her teeth yanked by the evil dentist-guy? Yeah. Like that. Blood everywhere for hours afterward.
I wouldn't go to a dentist for something like a decade after that. When I did, I found a nice doctor, but he gave me a pain pill that had the side-effect of inducing panic... this in a guy who wasn't real comfortable already. So there I was all alone (waiting for the pill to kick in) in the torture chamber -- I mean dentist's chair -- and suddenly my heart is racing, tunnel-ish vision ensues, and so on. GAWD.
Another experience: "Oh, you won't need pain medication for this. I only need to cut a small groove down the center of the tooth. You won't feel more than a little pressure." Later: "Oops, looks like we'll have to drill a bit deeper. But it'll be quick, no need for meds."
Yes, I do believe dentists choose their profession for wont of torturing people.