The Old Testament is not a perfect historical document, nor is it tuned to the sensibilities of 2012. In an argument about slavery over at Egnorance, I was confronted with biblical verses about slavery, marriage rights, child abuse and so on. I know of these, but they don't bother me as a Catholic. Further, I don't feel the need to look into why they're not important. I've read plenty of Catholic thinkers and every major question I've ever had has been answered to the point where it all makes sense.
Having found no glaring mistakes, I've assumed that other issues have been similarly well-addressed and have moved on to more interesting things like daisies, photography and soccer. Throwing Old Testament verses in my face doesn't do any more to me than statistical chemistry equations. I can't derive them and I may not even understand them, but I've no doubt that trustworthy people have worked them out and I can get on with life.
This brings me to the Mormons.
If you search the web for Mormon archaeology or Mormon biology contradictions, you quickly come to the conclusion that the Book of Mormon has no historical basis at all. This has hung me up forever. How can otherwise wonderful, rational people believe in this nonsense? Elephants in South America? Please. It's ridiculous. The Mormons have spent tons of money and done lots of excellent archaeology in the New World and have found nothing at all to validate Joseph Smith's claims.
Just as I don't bother finding out the Church's positions on Old Testament teachings, who's to say they don't simply punt on their stuff as well and just go back to what is relevant to them - behavioral and moral issues. Every Mormon I can think of from my own life has been a wonderful person - moral, hard working and a good friend. If they were Catholic, I'd be pointing to them as exemplars of our faith. My issues with Mormons aren't real, they're theoretical. I need to get over them.