Why? Why can't space expand much faster than the speed of light?

Supposedly the math checks out. I have a mathematics degree and did quite a lot of graduate courses, but I don't know the math here. We rely on peer-review and other experts in that field to vet the math, because there is no other way. I do not have the years of hard work to spend.

Your accountant analogy is apt.

Suppose every month money vanished from your business and could not be accounted for. Your accountant says, "Well, I didn't see the money being spent with my own eyes, but my theory is that someone is stealing from petty cash, because that's the only possibility."

It's irrelevant. Without doing the math, neither you nor I can really engage on this issue.

I might add that in areas of math where I am knowledgeable, there are constantly people denying the truth of easily provable things.

The number of people who have told me that 0.999... is not 1 is very large.

Simple questions like, "What is 1 - 0.999... equal to then?" get ludicrous answers like "0.00... [infinitely many zeros] 1".