What is it that makes you think that Mormon beliefs are any more outlandish than any other religion? Care to explain to me how a six hundred year old man gathered up two of every animal and carried them around on a boat?
I think those stories are pretty absurd, too.
But here's the difference.
The guy who wrote that down was not just making shit up. He was putting to paper legends that had existed amongst his people for generations. And while the literal story was kind of silly, historians do believe that there were frequent massive floods in pre-history that have put a flood story in nearly every mythology. (Probably because as the glaciers retreated after the last ice age, big floods were common.)
No, yeah, for the first 10 or so chapters of Genesis you have some silly legends, and then the rest is actually probably some history spiced up with some less impressive miracles because everything they didn't understand was "God".
No such wiggle room with Joseph Smith. There were no Golden Plates. The "Book of Abraham" Papyrus were found and determined to be not what he portrayed them as. The Kinderhook Plates turned out to be fakes made by Smith's neighbors. He was making it all up to con less smart people out of money and get into the bloomers of teenage girls.
And much like Scientology, the people who now run it know it was a scam, but they can't come out and say so, there's too much money to be made.
Which is why Romney squirms every time someone asks him about the Magic Underwear. He knows it's bullshit, but it's bullshit that benefits him.