And now, behold, if Adam had not transgressed he would not have fallen, but he would have remained in the garden of Eden.  And all things which were created must have remained in the same state in which they were after they were created; and they must have remained forever, and had no end.
And they would have had no children; wherefore they would have remained in a state of innocence, having no joy, for they knew no misery; doing no good, for they knew no sin.
But behold, all things have been done in the wisdom of him who knoweth all things.
Adam fell that men might be: and men are, that they might have joy.
2 Nephi 2:22-25, (emphasis added).

And from the Pearl of Great Price:

And in that day Adam blessed God and was filled, and began to prophesy concerning all the families of the earth, saying: Blessed be the name of god, for because of my transgressions my eyes are open, and in this life I shall have joy, and again in the flesh I shall see God.
And Eve, his wife, heard all these things and was glad, saying: Were it not for our transgression we never should have known good and evil, and the joy of our redemption, and the eternal life which God giveth unto all the obedient.
Moses 5:10,11, (emphasis added).

From these and other Mormon scriptures it is reasoned:

A key aspect of this rationalization concerns the ability to have children.  Mormon scripture, as seen above, states that Adam and Eve could not have children.  Given the importance of childbearing and family in the LDS church, this supposed inability is of paramount importance.  God could not advance the Mormon plan of salvation with a sterile humanity.

Mormonism incorporates this unique teaching in a unique definition for the word 'mortal'.  Christians and Mormons would both say the Fall made man mortal. Both agree that this means that man would now face physical death.  But Mormonism goes on to say that mortality also gave man the capacity to have children.  In Mormonism, mortal is defined as both the ability to procreate and the eventuality of physical death.  Dictionaries and the Bible do not support such a definition.

Given this reasoning, it is now not as hard to understand the teachings of  Mormonism concerning the Fall.

Some people believe that Adam and Eve committed a serious sin when they ate of the tree of knowledge of good and evil.  However, latter-day scriptures help us understand that their fall was a necessary step in the plan of life and a great blessing to all of us.  Because of the fall, we are blessed with physical bodies, the right to choose between good and evil, and the opportunity to gain eternal life.
Gospel Principles, p. 33 (emphasis added).

Adam and Eve were chosen to be the first people to live on the earth [see Moses 1:34].  Their part in the Father's plan was to bring mortality into the world... Adam and Eve were among our Father's noblest children.
Gospel Principles, p. 31.

The Fall was a "glorious necessity to open the doorway towards eternal life," said Elder Dallin H. Oaks of the Quorum of the Twelve Apostles.  Ensign, January 2002 "The Choice that began Mortality", p. 38 (emphasis added).

Former church president and living prophet Joseph Fielding Smith said: "it would have been a terrible calamity if they had refrained from taking the fruit of the tree..."  Quoted in Ensign January 2002 page 38.  However, all these rationalizations fly in the face of the words of the Bible.

For if, by the trespass of the one man, death reigned through that one man, how much more will those who receive God’s abundant provision of grace and of the gift of righteousness reign in life through the one man, Jesus Christ. Romans 5:17

If sin was never introduced into the world, then creation would still be perfect.  Mankind would be living in peace and harmony with each other, with nature, and with God.  Mormonism glorifies the introduction of pain, sorrow, war, plague, hatred, separation, desolation, decay, deceit, corruption, and filth into creation.  This is motivated by a self-centered desire to become a god.  Living eternally in a perfect creation with God provides no opportunity to become a god oneself.  It is ironic that this is the same self-centered desire that led Eve to eat of the apple (Gen 3:5).

We've seen that God's Word not does support Mormonism's depiction of the Fall.  We have also seen that Mormonism uses rationalizations to support its view.  Mormons routinely accept logical arguments (rationalizations) presented by their churches' authorities as proof of their doctrine.  Just as routinely, they will discount similar logical arguments presented by non-Mormons that disprove their doctrine; even arguments that apply their own logic.  For example, the Mormon logic used to depict the Fall is used in the following three statements.

Not surprisingly, Mormons  who accept as truth 2 Nephi 2:22-25 and Moses 5:10,11 would considered such statements foolish.  In addition, such statements do not result in Mormons questioning the doctrine supported by the same logic.  The insight into Mormonism that can be gained by recognizing this seeming contradiction is that Mormons are conditioned to accept rationalizations that are not necessarily universally applied.  This is part of the elastic nature of Mormonism.  Like doublespeak, inconsistent rationalizations make it difficult to directly debate Mormon doctrine.

This is a valuable insight.  Because of it, we can conclude that logically debating Mormon doctrine is not an effective tactic to witness God's Word to a Mormon.  This insight coincides with the biblical teaching that an unbeliever cannot come to faith by logic; rather, it is through the power of God's Word.