I certainly hope the next survey will ask how many of those saying they agree or disagree with it

Since our certainty was given as a percentage, none of us said we agreed or disagreed with it in the survey, unless you define "agree" as certainty > 50% and "disagree" as certainty below 50%

Or are you saying that we should default to 50%, in all cases we aren't scientifically qualified to answer of our own strength? That has obvious problems.

"So ask the question next survey. I do, however, strongly suspect they're expressing an opinion on something they don't actually understand"

That's like asking people to explain how consciousness works before they express their belief in the existence of brains, or their disbelief in the existence of ghosts.

I do, however, strongly suspect they're expressing an opinion on something they don't actually understand - and I don't think that's an unfair assumption, given most people don't - which would imply they were only doing so because "believe in MWI" is a local trope.

What is "actually understand" here and why does it sound like a dichotomy? Are you arguing that one cannot have any opinion about MWI based on any amount of understanding derived from popularizations (Eliezer-written or otherwise) which falls short of one being able to solve technical problems you list?

Surely you don't believe that one is not allowed to hold any opinion or confidence levels without becoming a full-fledged domain expert, but that does sound like what your argument is.

Your line of argument could equally apply to quantum physicists.