Just read Solemn Covenant by Carmon Hardy which deals mostly with Utah and post-manifesto polygamy. During these years there was no shortage of explanation given for the practice. It ranged from the oft heard and most simplistic, "God commanded it" to healthful benefits of polygamy vs. monogamy.
"God commanded it" is easy enough to say but hard to understand in that the revelation was recorded and made known to a small group in 1843 (some claimed to have known much earlier) BUT the practice was— according to some— to have started as early as the early 1830s. The 1843 revelation talks about the practice in terms of the sealing power but the Elijah didn't appear until 1836 so it's unclear how that would have worked. In any event, if we just go with God commanded polygamy, it must be admitted that the practice was important to God's kingdom. What other commandment can you think of that was enforced by an armed angel?
It was said in the Utah days that polygamists were more youthful and healthy than those who limited themselves to one wife. Offspring from plural marriage was said to be superior to that of monogamist as men weren't wasting their "vital fluids", as it were, on sex for pleasure, but instead it was focused on sex for procreation. Ironically, anti-polygamists in America at the time argued that offspring created by practicing the principle were inferior beings and sometimes implying they were even less than human.
In defense of the practice late 19th century/early 20th LDS also claimed the the practice kept society more moral. Men had/have a greater sex drive and so pairing them with more than one woman in marriage kept them from fornication and societal ills such as prostitution. Women wanted a provider and to care for children so according to the polygamist logic both men and women got what they naturally needed/wanted.
Many if not most understood the practice to be tied to the level of exaltation they received in the eternities as more children and wives in mortality equaled more posterity in the hereafter and thus a greater dominion. In fact many were convinced that plurality of wives was the form of marriage that God practiced and thereby populated His worlds. They practiced "patriarchal marriage" to do the works of Abraham and by doing so become like God.
The too many women argument is as far as I can see was never really used to justify the practice in the late 19th and early 20th centuries. Church leader John A. Widtsoe spoke put against this theory in 1943.
http://www.wivesofjosephsmith.org/Why.htmThe explanation that Joseph Smith, like many other powerful men, found a way to be with more women either for sexual or power reasons, makes the most sense to me. Did he create the practice to convince himself or his followers or the women? I don't know. I however do think sex and power were the main motivations behind it. You can see the same pattern repeated over and over through history.
The process that lead to ending the process was just as unclear. In fact what is considered the revelation (Official Declaration 1) to end practice today was not considered authoritative by virtually all of the leadership and at least a good portion of the membership despite the narrow approval in conference in 1890. Essentially it was a show put on for the US Government. It is clearly documented that from 1890 to 1910 there were still plural marriages approved and performed in the Church— and not just by renegade members or leaders. Eventually the leadership delegated the authority to lower leadership so they could truthfully say they were unaware of plural marriages while allowing them to continue. Only as monogamist came up in leadership and polygamist died off did the practice really end and become the red-headed step-child it is now (no offense meant to red-headed step kids).
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