On a subject like physics and MWI, I wouldn't take the explanation of any non-professional as enough to establish that a contrarian position is "obviously correct". Even if they genuinely believed in what they said, they'll still only be presenting the evidence from their own point of view. Or they might be missing something essential and I wouldn't have the expertise to realize that. Heck, I wouldn't even go on the word of a full-time researcher in the field before I'd heard what their opponents had to say.

On a subject matter like cryonics I was relatively convinced from simply hearing what the cryonics advocates had to say, because it meshed with my understanding of human anatomy and biology, and it seemed like nobody was very actively arguing the opposite. But to the best of my knowledge, people are arguing against MWI, and I simply wouldn't have enough domain knowledge to evaluate either sort of claim. You could argue your case of "this is obviously true" with completely made-up claims, and I'd have no way to tell.