Yeah, the internet is an echo chamber. You get lots of bad advice here. And urban myths are regularly being upvoted to no end. Especially here on Lemmy.
Usually a doctor should know things, they studied medicine for years.
And there are people with certain attitudes... People who only respond well to arguments of authority... And people who have a different perspective on subjectivity/objectivity and the factual world. Lots of people just want to believe something. And they'll search for any fake news supporting them or letting them believe whatever supports what they're set on.
I'd say if you're intelligent and know how to do research, and have the time to do so, look up things and learn things. If you can't do that: Stick with authority.
And most importantly: Don't ask on Lemmy or Reddit if you don't want to talk to random people and listen to them.