Does it not depend on the chemical composition of local water? The US is vast, geologically diverse, and water quality varies hugely across it. Denmark can likely make a decision that's good for the entire country.

Actually, what most countries seem to do (according to other comments I’ve seen here), is just delegate to local bodies, so country size is a complete non-issue.

It could, what do you have in mind with regards to chemical composition that may require fluoride in some circumstances?

And are those conditions manmade? If so, would we be better off reversing the proximal issues rather than adding fluoride to try to fix it?

a decades long study with a gazillion of potential confounders is never "either scientifically shown to be beneficial or it isn't"...

let alone the precautionary principle in a complex system with a gazillion variables... (i.e. things we don't know we don't know)