they already gave their explanation. if you disagree then it is on you to provide a counter argument otherwise anyone could just shoot down any argument by claiming that it has no merit.

at best you could say that you do not find the argument convincing, but even then you should explain why. you are not even claiming that the argument in question is wrong, you are only questioning the credentials of the author. that's appeal to authority, and therefore not a valid argument. https://youtu.be/N5k4yUSPHI8

I don't know much about microbiology, but that shouldn't stop me from asking someone who "did their own research" to shut up and let the experts talk.

yes it should, unless you can provide a convincing argument that the person is wrong, expert or not.

on the internet anyone can claim to be an expert and nobody can prove it.