To actually make this thread educational, let's give out valuable info:
Historically and theologically speaking fundamentalist Mormons are correct, since Joseph Smith never denounced the practice of plural marriages.
Nope. As I wrote above, LDS doctrine says that polygamy is "not OK" unless specifically sanctioned by the Lord. Joseph Smith translated the Book of Mormon, in which this doctrine is specifically found:
Jacob 2:27-28
27 Wherefore, my brethren, hear me, and hearken to the word of the Lord: For there shall not any man among you have save it be one wife; and concubines he shall have none; 28 For I, the Lord God, delight in the chastity of women. And whoredoms are an abomination before me; thus saith the Lord of Hosts.
And then a few verses later, the Book of Mormon qualifies this doctrine, effectively saying that if the Lord wants to use polygamy to "raise up seed" unto Him, He will command it. Otherwise, it is forbidden as an abomination. If you want to say Joseph Smith never denounced plural marriage, you have to ignore these verses in the Book of Mormon:
Jacob 2:30
For if I will, saith the Lord of hosts, raise up seed unto me, I will command my people; otherwise they shall hearken unto these things.
It was a political decission, part of the winning of statehood for Utah at the end of the 19th century.
Specifically, the President of the Church received a revelation telling him that if polygamy was not stopped, the Church's assets would be seized by the federal government. And the saints (members of the Church) are commanded to obey the law of the land, so polygamy was officially stopped.
Even decades after the church officially ended the practice, even the highest leaders of the LDS were still practicing it.
See Reed Smoot case if you are really interested in the topic.
See the following link for an explanation of this point:
Polygamy After the Manifesto
Otherwise the Mormon god is the most flexible one. He keep changing the location of Zion and other basic tenets (priesthood 1976, polygamy) according to the current political power and situation. I like that...
End of history lesson...
The doctrine of polygamy has not changed; it is expected to be reinstituted after the Second Coming of Christ. The practice is what was stopped. As for the priesthood ban, it was always expected that blacks would one day hold the priesthood, and that day came. We're not sure why they were denied it in the first place, and there are several good theories about that, but that is beyond the scope of this thread.