There has been an ocean of speculation as to why Mitt Romney doesn't reveal his last decade or so of tax returns, and with them a picture of his finances. Most of the speculation is political, along the lines of: if Romney fights this hard to hide his tax returns they must show a) his wealth was much greater than previously thought; and/or b) his taxes were much lower than previously thought; and/or c) his returns don't jibe with what is known about his off-shore holdings so he might be in serious legal danger.
I think something is being missed here: the Mormon connection. Some authors have commented on his contributions, perhaps even tithes, to the LDS. That is objectionable to many because of the Church's fights against marriage rights, abortion, etc. But the problem Mitt faces is, I believe, much more intimate. He grew up in the Mormon hierarchy, went to school and summer camps with the sons of the Apostles and the Mormon mega-rich, and is related in at least a shirt-tail way to many of them. He has undoubtedly cut them in on many of his most lucrative Bain deals, the ones that would be most embarrassing and even dangerous to disclose. If he were to reveal a broad picture of his finances, he would bring down not only himself but much of the LDS mega-rich leadership class. This would shake Mormonism to its foundation, and with it the Romney family and their entire world.