Why I do not believe

After leaving the Mormon church, I began questioning everything it taught me. One of these things is that marriage is only between one man and one woman. The thing that troubled me about this is that the Mormon church has a history of the opposite. It has indoctrinated marriage between one man and multiple women, or polygamy. In fact, it has historically taught that monogamy will ruin nations and is immoral. In the proclamation to the family; it's current stance is the opposite of its previous belief system:

"It is a fact worthy of note that the shortest lived nations of which we have record have been monogamic. Rome...was a monogamic nation and the numerous evils attending that system early laid the foundation for that ruin which eventually overtook her."
- Apostle George Q. Cannon, Journal of Discourses, Vol. 13, p. 202

"Since the founding of the Roman empire monogamy has prevailed more extensively than in times previous to that. The founders of that ancient empire were robbers and women stealers, and made laws favoring monogamy in consequence of the scarcity of women among them, and hence this monogamic system which now prevails throughout Christendom, and which had been so fruitful a source of prostitution and whoredom throughout all the Christian monogamic cities of the Old and New World, until rottenness and decay are at the root of their institutions both national and religious."
- The Prophet Brigham Young Journal of Discourses, Vol. 11, p. 128

"...the one-wife system not only degenerates the human family, both physically and intellectually, but it is entirely incompatible with philosophical notions of immortality; it is a lure to temptation, and has always proved a curse to a people."
- Prophet John Taylor, Millennial Star, Vol. 15, p. 227

"Monogamy, or restrictions by law to one wife, is no part of the economy of heaven among men. Such a system was commenced by the founders of the Roman empire....Rome became the mistress of the world, and introduced this order of monogamy wherever her sway was acknowledged. Thus this monogamic order of marriage, so esteemed by modern Christians as a holy sacrament and divine institution, is nothing but a system established by a set of robbers.... Why do we believe in and practice polygamy? Because the Lord introduced it to his servants in a revelation given to Joseph Smith, and the Lord's servants have always practiced it. 'And is that religion popular in heaven?' it is the only popular religion there,..."
- The Prophet Brigham Young, The Deseret News, August 6, 1862

"This law of monogamy, or the monogamic system, laid the foundation for prostitution and the evils and diseases of the most revolting nature and character under which modern Christendom groans,..."
- Apostle Orson Pratt, Journal of Discourses, Vol. 13, page 195

"We breathe the free air, we have the best looking men and handsomest women, and if they (Non-Mormons) envy us our position, well they may, for they are a poor, narrow-minded, pinch-backed race of men, who chain themselves down to the law of monogamy, and live all their days under the dominion of one wife. They ought to be ashamed of such conduct, and the still fouler channel which flows from their practices; and it is not to be wondered at that they should envy those who so much better understand the social relations."
- Apostle George A Smith, Journal of Discourses, Vol. 3, page 291

"I have noticed that a man who has but one wife, and is inclined to that doctrine, soon begins to wither and dry up, while a man who goes into plurality [of wives] looks fresh, young, and sprightly. Why is this? Because God loves that man, and because he honors his word. Some of you may not believe this, but I not only believe it but I also know it. For a man of God to be confined to one woman is small business. I do not know what we would do if we had only one wife apiece."
- Apostle Heber C. Kimball, Journal of Discourses Vol 5, page 22

"Just ask yourselves, historians, when was monogamy introduced on to the face of the earth? When those buccaneers, who settled on the peninsula where Rome now stands, could not steal women enough to have two or three apiece, they passed a law that a man should have but one woman. And this started monogamy and the downfall of the plurality system. In the days of Jesus, Rome, having dominion over Jerusalem, they carried out the doctrine more or less. This was the rise, start and foundation of the doctrine of monogamy; and never till then was there a law passed, that we have any knowledge of, that a man should have but one wife. "
- The Prophet Brigham Young, Journal of Discourses Vol. 12, page 262


By the way, Brigham Young, according to the bible, which you believed in, monogamy was introduced on to the face of the earth with Adam and Eve. 

The Mormon Church is its own enemy. It does not need to look to anti-mormon sources as its enemy, but within its own boarders.