I find it rather hilarious that people point at those nasty Mormons voting for Romney because, *gasp*, he’s a Mormon. These same people voting against him for same said reason are unable to see the irony.
By your logic, I should not support Santorum. I, as a Puritanical Calvinist, think Roman Catholicism is a heretical belief system that does not preach the true Gospel. However, I do support Santorum in spite of his conservative Roman Catholicism. Why? Because he shares at least somewhat similar political goals. If a Mormon ran that shared my political goals, I would vote for him. I suppose, if all other things were equal, I would vote for a fellow Evangelical Protestant over others simply because they were a fellow Evangelical Protestant. That is only with everything else being equal, however.