My two concerns are that, you wouldn't hold the vapor in your mouth long enough for it to actually be helpful, and with some people vaping occasionally, and others doing it constantly, it would be difficult to keep the fluoride levels high enough for casual users to get a benefit, but low enough that all-day every-day folks don't OD.
I can tell you of one adult guy who went to Germany with no cavities, lived there for two years, and came back with several cavities. Not, like, a couple cavities, but several. Germany doesn't flouridate their tap water.
That guy was me, and now whenever I hear fucknuts complaining about flouride in tap water in the US, I stick 'em in the mental "dumb-asses not worth listening to" bin.
I don't think the claim is that it's deadly; I believe the concern it's that there's little to no proven benefits when used topically and at least a few proven detriments when ingested. I haven't done much reading on the subject, so I'm not sure.
Regardless of the veracity of the aforementioned claims, I believe it's immoral for a government to add unnecessary chemicals to public water supply.
Why make them illegal? I used a vape to limit my nicotine intake and weaned myself off of smoking (and vaping) completely. It still sucked for the first 6 months and the occasional random craving that comes from being a smoker for over a decade, but at least I fought each part of the smoking addictions separately which made it bearable.
For clarity, I got 0% nicotine vape juice for a month or so before I quit puffing completely so let the withdrawal from the substance run its course, and then had to deal with the psychological side of things. Which was VERY annoying. Everytime I'd do anything where I'd normally smoke triggered a craving.
What we REALLY need to do is limit the concentration of nicotine in vape juices to no higher than that found in a "standard" cigarette. Part of the problem right now is that you can easily buy vape juice with waaaay more nicotine per puff than any tobacco product so it's much easier to get addicted.