I'm not saying your wrong, just that the level of confidence in your assertions is not warranted.
But that is sort of the point of science, you take all the evidence you have and create a hypothesis and iterate as you get more evidence. If I find evidence that suggests something else then I will be happy to tweak or abandon this. My level of confidence comes from the existing evidence and lack of evidence otherwise.
It is a tale as old as time. See the story behind the term. ultracrepidarian: https://en.wiktionary.org/wiki/ultracrepidarian#English
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.
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.)