There are clear factual errors in the underlying assumptions of what was stated about water fluoridation. Those are simply table stakes for having a discussion about anything at all. If one thinks that water fluoridation is useful "just for a few seconds," that it's not done outside of the United States, that it's a replacement for toothpaste, that it's a vital chemical, or that we don't fortify other foods, then they do not know enough about the topic to talk about it, let alone hold the opinion that they know
better.
If someone came in with a curious mindset, that'd be one thing. But this is someone walking into a room with an agenda (get rid of fluoride) and a shocking lack of knowledge about that agenda.