One of the darkest moments in Utah and Latter-day Saint history is the practice of slavery in the Deseret area, beginning with the passing of the Act in Relation to Service (February 4, 1852) until June 19, 1862 when the US Congress prohibited slavery in all US territories.
Albert E. Bowen (1875-1953), at the time of the publication of his book, Constancy Amid Change, a member of the Council of the Twelve Apostles, commented on the capitulation of Christian churches on the question of slavery; while not including The Church of Jesus Christ of Latter-day Saints, it would be wise to realise that, on this issue as well as the temple/priesthood restriction, the LDS Church would fall under such condemnation (and rightly, too):
If you want an example take the case of slavery. By and large the ministry did not condemn it so long as the institution was powerful. But if slavery was wrong it was just as wrong when in the bloom of its power as it was when attacked by the forces that crushed it, and it just as much merited the condemnation of the church. There could be only one result. The church became servile, opportunistic, worldly, a faithful counterparty of the society which it served. It lost most of its own self-respect and it did not command the respect of the laity. Men drew their convictions from their own practices and habits, the prevailing usages of their times. It is as if man had lifted the ideals of contemporary life bodily out of their setting and had transferred them over to himself and made them his every day religion, the only religion which for him had any reality. He became thoroughly saturated with the materialistic spirit of the age. He was its product. The society in which he lived made its own moral standards restrained only by conventions. For him practices have dictated principles; what he does has determined what he believes. (Albert E. Bowen, Constancy Amid Change [Salt Lake City: The Deseret News Press, 1944], 51-52)
Sadly, in many quarters (e.g., here in Ireland), many members (including leaders) have capitulated on the topic of abortion and have demonstrated the same spinelessness many 19th century church members and leaders on slavery, both moral evils.
For the best discussion of the history of blacks in the Church, see:
Russell W. Stevenson, For the Cause of Righteousness: A Global History of Blacks and Mormonism, 1830-2013 (Salt Lake City: Greg Kofford Books, 2014)