Mitt Romney wants voters to give him a pass on revealing the content of his tax returns because facts about his contributions to The Church of Jesus Christ of Latter-day Saints should remain only between him and the church. The LDS Church, after all, does not discuss the contributions of its members, even with other members, he points out.
There is just one rather large flaw in his reasoning. Other church members are not candidates for the office of president of the United States. Romney is.
It seems obvious that, when you seek the highest elected office in the land, you give up the normal expectations of privacy that the rest of us enjoy. Romney's father in 1967, when he was running for the same office, released more than a decade of his tax returns so that voters could better understand his business dealings and other "private" information they might use to decide for whom to vote. George Romney, also a Mormon, did not use the "tithing is private" argument.