The New York Times has a well done, lengthy article ("What Is It About Mormonism?") [HT Mormon Stories] discussing the church's need for, and use of secrecy from it's inception to today. It argues that Romney's candidacy has opened another such chapter, needing to represent itself as mainstream Christians in order to avoid the "soft bigotry" in American politics. I've included a few excerpts below, but the entire article is worth reading.
"Mormonism's political problem arises, in large part, from the disconcerting split between its public and private faces. The church's most inviting public symbols — pairs of clean-cut missionaries in well-pressed white shirts — evoke the wholesome success of an all-American denomination with an idealistic commitment to clean living. Yet at the same time, secret, sacred temple rites and garments call to mind the church's murky past, including its embrace of polygamy, which has not been the doctrine or practice of the mainstream Church of Jesus Christ of Latter-day Saints, or LDS, for a century. Mormonism, it seems, is extreme in both respects: in its exaggerated normalcy and its exaggerated oddity. The marriage of these opposites leaves outsiders uncomfortable, wondering what Mormonism really is."
"Like Mormon ritual, much of Mormon theology remains relatively inaccessible to outsiders. The text of the Book of Mormon has always been spread to a broad audience, but the text is not a sufficient guide to understanding the details of Mormon teaching. Joseph Smith received extensive further revelation in the nature of sacred secrets to be shared with only a handful of close associates and initiates within the newly forming church."
"Growth brought publicity — and with it came not merely prejudice but outright persecution. This external persecution created a second, externally driven source for secrecy: protection."
"The Mormon path to normalization over the course of the 20th century depended heavily on this avoidance of public discussion of its religious tenets. Now that plural marriage was out of the picture, the less said the better about the particular teachings of the church, including such practices as the baptism of the dead and the doctrine of the perfectibility of mankind into divine form. Where religious or theological conversation could not be avoided, Mormons depicted themselves as yet another Christian denomination alongside various other Protestant denominations that prevailed throughout the United States."
"If 19th-century Mormon secrecy was a matter of survival, 20th-century Mormon reticence was a form of soft secrecy, designed to avoid soft bigotry. Revealing Mormon teachings would no longer have led to lynch mobs or federal arrest, but it certainly would have fueled the kind of bias that keeps politicians out of office."
"Faced with the allegation that they do not believe in the same God as ordinary Protestants, or that their beliefs are not truly Christian, Mormons find themselves in an extraordinarily awkward position. They cannot defend themselves by expressly explaining their own theology, because, taken from the standpoint of orthodox Protestantism in America today, it is in fact heterodox."
"What is more, what began as a strategy of secrecy to avoid persecution has become over the course of the 20th century a strategy of minimizing discussion of the content of theology in order to avoid being treated as religious pariahs. As a result, Mormons have not developed a series of easily expressed and easily swallowed statements summarizing the content of their theology in ways that might arguably be accepted by mainline Protestants. To put it bluntly, the combination of secret mysteries and resistance in the face of oppression has made it increasingly difficult for Mormons to talk openly and successfully with outsiders about their religious beliefs. "
"If the reality of soft bigotry does not today pose an existential threat to Mormons as explicit oppression once did, it would nevertheless undercut the hard-won public face of Mormonism as a distinctively American religion characterized by worldly accomplishment. For conservatives to reject a Mormon because he is a Mormon would be an especially harsh setback for a faith that has accomplished such extraordinary public success in overcoming a history of painful discrimination."