You may think the "why" questions are ultimately meaningless and irrelevant
No, I don't think they are meaningless or irrelevant. I think people create the 'why' answers to make themselves feel better about things. That's not the same as being meaningless. For me the 'why' assertions only make for a more sinister world, because then I have to wonder about the 'why' of an Ebola virus, or of tsunamis or typhoid. But some people find the 'why' assertions comforting, and they're welcome to them.
God had previously been offered as an answer to "why" the world exists, or as to why the world is at it is, rather than some other way. But the mere existence of God doesn't answer that--you're still stuck with contingency.
our space-time dimension might not be the center of time.
And I did not say it was. In any case, further understanding, should we attain it, of the dimensionality or extent of space, time etc will come through science. At no point did I indicate that our current, tentative models were final, or represented 'ultimate' reality or anything of the sort.
it is mostly opinion
Do successes of science, the fruits of the model, all our technological advances, indicate that it's all pretty much just opinion?
if you accept the many worlds theory of quantum mechanics
I don't actually know either way. Deutsch made a strong argument for the MWI in The Fabric of Reality, but all scientific findings and theories are tentative. And I didn't call anyone an idiot.
True, but we're also hopping between meanings of the word 'world.' Like 'universe' it can mean 'everything that exists' or 'a given sphere of spacetime.' Probably other meanings I missed, too. We haven't even touched on Everett's Many-worlds interpretation of Quantum Mechanics, which David Deutsch made a great case for in The Fabric of Reality. The MWI of QM doesn't replace the plurality of worlds (spheres of spacetime) popping out of the inflationary models, rather it... complements it? Duplicates it? Subsumes it? Not sure where that rabbit hole leads. Any ideas?