Final answer:
The Mormon belief that was most offensive to people was plural marriage, or polygamy, along with the tendency towards a quasi-theocracy and new divine revelations which led to distrust and conflicts.
Step-by-step explanation:
The belief of the Mormons that was most offensive to most people during the time of the Latter Day Saint movement's emergence was plural marriage, also known as polygamy. This practice, whereby Joseph Smith and other Mormon leaders had multiple wives, attracted significant attention and outrage across America. It was perceived as a challenge to the conventional norms of marriage and was one of the key reasons for the intense persecution and opposition that the Mormon community faced. Additionally, the autocratic nature of Mormon leadership and their tendency to form a quasi-theocracy through block voting and strong community laws also caused concern among non-Mormons. These practices, along with the claims to receive new divine revelations, led to distrust, skepticism, and conflict, culminating in the murder of Joseph Smith and the eventual westward migration of the Mormons under the leadership of Brigham Young.