I will not claim to be an expert on this subject, so I'll add a link to thoughts of men of far greater intellect than myself, but as this comes up again and again when people speak about Mormons I'm going to add my own thoughts on the matter, and how I feel the evidence stack ups.
Firstly, plural marriage is a fact in the history of the Church of Jesus Christ of Latter-day Saints, but for the modern day Church is it only that - history. It doesn't really affect anyone who is a member of the Church here in 2013. Though some use it as an excuse to leave the Church when they hear about it is frankly stupidity of the highest order.
Secondly, Joseph Smith was married to other women at the same time he was married to Emma. Though this fact is unpalatable to some, it doesn't take away the fact that Joseph was a Prophet, it doesn't mean the First Vision didn't take place, it doesn't nullify the Book of Mormon, or anything else. It isn't really a hidden fact either. If you look up Joseph Smith's entry in the Church's genealogy website, New Family Search, the information is there for all to see - I know, I checked.
For those who cry, "But it's not in the Church manuals. There's no mention of Joseph’s plural marriages." It isn't the Church's job to teach you this information. The Church's job is to bring people to Christ, members marital arrangement, even Prophets', don't do that.
The truth is we don't really know what life was like back at the beginning of the Restoration, so solutions to life's day-to-day problems are hard to understand for us looking back over 160 years or so. The claim that Joseph introduced plural marriage because he wanted to have sex with lots of different women, including girls as young as 14, really doesn't stand up to what the evidence shows. I mean, since when has being married meant more sex? And where did he find the time for all this sex he is supposedly having? That line of thought just goes to show that some people can't look past their own 'natural man' mentality.
Yesterday, BYU Professor, Dr. Daniel C. Peterson, posted on his blog about an article by Dr. Brian Hales examining what Joseph Smith's plural wives thought of the Prophet after his death. If anyone had a right to complain about this whole issue, they did. But guess what, it turns out they didn't. Dr. Hales says:
“none of Joseph Smith’s plural wives ever accused him of abuse or deception, including the seven who did not gather to Utah with the main body of the Church. Decades after their feelings had matured and their youthful perspectives were expanded by additional experiences in subsequent marriages, it appears that none of them claimed they were victimized or beguiled by the Prophet. None came forth to write an exposé indicating he was a seducing impostor or claim that polygamy was a sham or a cover-up for illicit sexual relations. Even mild criticisms seem to be absent in the historical accounts and reminiscences of the Prophet’s plural wives. It seems that if any of Smith’s polygamous wives eventually decided that he had debauched them, their later scorn might have motivated them to expose him through the press. Certainly, numerous publishers would have been eager to print their allegations.”
To find out more about the article go to Dr. Peterson's Blog:
Personally, I feel that God called the Prophet to practice plural marriage for a specific reason, at a specific time, but didn't tell him how to implement the practice into 19th Century America. Did Joseph and others who were asked to participate in plural marriage make mistakes with the principle? Probably. The introduction at the same time of Eternal Marriage sealings (see Doctrine and Covenants section 132) blurred the line then, as it does for some people now who can't tell the difference between the two and either continue to practice it, or say that the Church should practice it but the Lord doesn't think we are ready and able to. The scriptures tell us that plural marriage can only be practiced when the Lord allows, and is the exception rather than the rule. Most Mormons in the 19th Century didn't practice plural marriage, but were still considered worthy members of the Church. To believe that plural marriage was (and still is) essential for exaltation is a serious misreading of both scripture and the words of General Authorities on the subject.