Science denial

I am so tired of people thinking they know better than professionals when they don't even have basic knowledge on the topic.

I'm a student in dental hygiene who recently argued in a YouTube comment section with a guy who had said that if fluoride was effective, we wouldn't be seeing such high rates of gum illnesses in the population. Not what fluoride is for. Not even close. I took the time to explain why, but no reply.
Then another person jumped in. They were on my side, but claimed fluoride only works when ingested and not through topical applications like toothpaste. Not true. I had to correct them too, but still: no reply. No reply to me, but the two bozos keep arguing with each other for days. Misinformation against misinformation.

Why are we so stupid?