Someone participating in this discussion would either know this from general knowledge, or could look it up.
People aren't that ignorant.
You have only to look up the rates of tooth decay among non-fluoridated countries to find that there is no difference whatsoever.
It doesn't matter what theirs is, the link I gave you isn't useful as a source, but as a list of sources.
Therefore, "anti-fluoride" seems fitting.
If you must dispute water fluoridation on Hacker News, do so by making careful, factual, respectful comments.
The site guidelines specifically ask you not to call names. That includes both calling each other names as well as calling each others' arguments names (e.g. "woo").
I'm not sure how any of this relates to vaccines, since we are talking about fluoride. But anytime you want to know if something is true or not, the only way I know of is to dig deeper for more information.
One thing to keep in mind while digging in, we know there is a financial incentive behind pro-fluoridation studies (it is expensive for business to dispose of it). As far as I know, there isn't much financial incentive in being against fluoridation, save for some boutique toothpaste brands that would probably lack the resources to conduct peer reviewed studies.