Why do people post answers that are clearly "urban legend" then claim to be authorities on the subject?

I don't think your question is a rant, as someone else posted! You raise an issue which needs to be addressed. There needs to be some disclaimer or something about using caution and common sense whether it is a doctor in a hospital or an anonymous person claiming to be a doctor or med student. As irisiris mentioned, even if a person really is a doctor or med student, it doesn't mean their advice is always completely accurate or up to date.