Comment by kebman

It isn't. But as a society, we voted for providing clean, affordable water to everyone was a public good. That's why municipal water exists.

The issue arises when that water is fluoridated against the will of a significant portion of the population. It effectively forces dissenters to either accept it or go through the hassle and expense of sourcing their own water — which defeats the original purpose of providing low-cost, universally accessible water.

Today, the marginal benefits of fluoridation are questionable, especially with fluoride available in toothpaste. So forcing it on everyone, despite objection, becomes harder to justify — and that's why some places have stopped adding it.