My foray into the politics of fluoride on Cape Ann didn’t start off smoothly.

On Thursday night, as I settled into one of the back rows of a community forum put on by the Rockport Board of Health, an anti-fluoridation activist one seat over turned my way. “Are you a shill?” she asked. Indicating my notepad, she added, “Taking notes for the dental people?”

Until recently, the fluoridation of drinking water to prevent tooth decay — a measure supported not just by the American Dental Association but also a variety of other public health organizations — seemed like a settled issue in much of Massachusetts. But it’s reemerged as a controversy in Rockport and Gloucester, where a group called Cape Ann Fluoride Action Network has touted a range of potential health risks. Rockport votes Tuesday on a measure to stop the practice. Gloucester has a vote scheduled in November.

These referendums highlight the impact a small group of dedicated believers can have in a democracy. They also hint at a mounting tension between public health measures, which require some faith in credentialed experts, and the expectation that, in a do-it-yourself kind of society, individual citizens have to figure things out on their own.

On Cape Ann, the fluoridation fight has played out in dueling letters to the editor in the Gloucester Times, and it’s plainly a source of frustration for local health officials. In Rockport, Board of Health chairman Dr. Sydney Wedmore invited only pro-fluoridation speakers to Thursday’s forum. “I put together a panel that I felt could present the most up to date scientific information possible,” he said in an interview, noting that virtually the entire medical and dental community of Cape Ann signed a letter supporting fluoridation.

Yet nothing in American life today socializes us to trust large organizations or rely on others’ help or professional expertise. People are expected to serve as their own pension funds, act as their own financial advisers, and manage their own personal brands. Using tools on the Internet, you can guess at your own medical condition and write your own will. This mindset also shapes our politics: Some Tea Partiers carry pocket Constitutions. It’s as if, even in matters of interpreting the law, everything’s all up to you — and you’d better keep your guard up.

After the meeting in Rockport, I spoke with several members of the Cape Ann anti-fluoridation group, who’d come to the issue in different ways; one of them, Inge Sullivan, cited a lifelong belief in natural foods and natural remedies, while others cited relatives with symptoms they attributed to too much fluoride.

But they all emphasized the effort they’d invested in studying up on the issue. Members of the group bristle at being likened to anti-vaccine activists, and at the insinuation that they don’t know how to separate good information from bad. “Just because it’s off the scary Internet,” said Luke Ellis, “doesn’t mean it’s not true.”

An individual word on a screen starts to look funny if you stare at it too long; maybe the same is true of public health measures, too. I clicked through the long list of citations that one anti-fluoridation activist had sent along, and soon enough was drowning in studies whose significance was entirely murky, at least to me. In these situations, throwing up your hands and relying on trained professionals isn’t a surrender. It’s a survival tactic.

From time to time, the experts are misguided, resistant to change, or flat-out wrong. But usually there’s peace of mind in trusting them.