Correction. Toxic at high concentrations
Ok, just because you say it doesn't make it true. However I must admit that it is at least partially swayed in such a way. That is enough for the effect you describe. Here you can describe opportunity. That is not enough.
And that its cheap, easy to apply, safe, and effective (I'm not clear on the effectiveness, so I will not make this claim personally, I only am saying that many people do claim it to be effective. That is in debate).
I don't think the government could ban something that is a proprietary claim in that way. Yes it degrades teeth, but the risk is known to the people. It is the peoples responsibility to drink it or not. However, the government can make an add on to the water that can help. Especially if it's so very cheap.
You do know that fluoride occurs naturally, including in spring water because of the natural filtration of limestone. Some bottled waters of fluoride, some do not. Depends on if the source naturally has fluoride and if there is fluoride added.
People can buy filters to eliminate fluoride from their drinking water. They have a choice. The information is available. I read on somewhere that it is not dissimilar to the way that regulations require helmets on bikers or seat belts in cars. Something about when the risk is nonexistent or minimal, and it improves public health/safety, then the government can legally make such a change. Fluoride falls in those requirements. And there is nothing unethical considering how easy and cheap fluoride filters are.
Look, if you want to through a fuss over something this minimal, you can. To me, I have no worry. You should be so lucky to worry about this. You don't have to worry about parasites, bacteria, or other far more toxic substances. You get clear water. A lot of naturally occurring water has fluoride in it anyways, and the human race isn't dead yet. It's not a problem. Technically, people have lived with fluoridated water for a very long time.