Throwaway because I run a large dental software company. Dentistry is practiced as a business focused on maximizing revenue. Dentists are routinely coached to deploy sales tactics to increase their treatment acceptance beyond what is needed. If you walk into a dental office, you need to protect yourself from being abused. A second opinion unfortunately puts you in the same position, but now with a new dentist who wil…
If my experience is as ubiquitous as I suspect, there seems to be a perverse incentive among dentists to allow adults to ruin their own teeth. It's convenient because most people know extremely little about dental health beyond brushing and flossing. A minor carie on the enamel doesn't necessarily progress further than surface damage, and in some cases can even be reversed. Instead of saving the patient time and money by waiting for further progression of a carie, many dentists see the tiniest surface divot as an opportunity to drill n' fill. A more appropriate response would be to suggest the patient eat an appropriate diet that doesn't feed carie-causing bacteria and to come back in 6 months to a year for a follow-up; if the carie is visibly worse, then now it's time to consider drilling.
In defense of dentists, I imagine so few adult patients are compliant with suggestions of lifestyle changes that they figure it's hopeless and they might as well be the ones to cash in on cavities rather than some other dentist. Everyone hates going to them and they know they can't win.