Earlier quoted context omitted.
Versus https://en.wikipedia.org/wiki/Argument_from_authority See also: https://www.science.org/content/article/potential-fabricatio... Amateur's asserting their opinions as facts isn't great, but epistemologically it's no worse (and systemically, like less harmful) than when the experts do it.
Experts, when given the chance, have a tendency to speak with nuance and describe the degree of confidence they have in different statements. Compare this with an amateur writing with certainty about a subject that subject matter experts continue to debate after decades of work. I know which one of the two I would rather bother listening to.
Saying that experts are less likely to do X doesn't say anything about the relative harm of their doing so. If some rando on the streets is shouting their opinion about what causes Alzheimer's and asserting it's God's Own Truth, it's going to cause less overall harm that a carefully worded (but equally wrong) statement from an expert. (And the fact that we tend to hold experts in higher regard is the reason we should be more concerned about them stating their opinions as facts than about amateurs doing the same.)