People listen to his word on things because he’s been working in dentistry for 40 years, he’s primarily the one who started spreading the concept of mewing in the first place, he wrote a book about it, & has a YouTube channel based around it. Therefore I think it’s reasonable to assume that he at least has a decent understanding of the concept. Which is probably why people take his word on a lot of things. Not because he’s a deity, but because based off his experiences revolving around orthotropics he’s probably very well informed.

Personally I haven’t seen any of the comments that you’re talking about. (Could you provide some example maybe?) Most of the comments that I see that actually get upvotes that could be labeled as “harsh” are just constructive criticism comments or comments that are just answering a question honestly, anyone who’s actually just being blatantly rude/insulting the OP, usually doesn’t get upvotes. (No one has as far as I’ve seen.)

Have you seen people saying that having bad teeth or mouth breathing was the OP fault? On a different account I made a post about how I was mouth breathing in my sleep and all I got was genuine answers and advice from people. Not that it doesn’t happen, but I haven’t seen any of it.