See also: Exodus 20:14
The only legitimate employment of the power of procreation is between husband and wife, man and woman, who have been legally and lawfully married. Anything else violates the commandments of God. From Alma, “If ye speak against it, it matters not, for the word of God must be fulfilled.” (Alma 5:58) — Boyd K. Packer, “Our Moral Environment,” General Conference, April 1992
Adam and Eve had been in a state of stagnation: no progress—no growth—no reproduction. Without a change, they would have remained in that state forever. It was necessary for a change to take place. This change meant that Adam and all his posterity would have to work and overcome obstacles to provide the necessities of life. — Eldred G. Smith, “Opposition in Order to Strengthen Us,” General Conference, October 1973
God commanded each living thing to reproduce after its own kind (see Genesis 1:22). Reproduction was part of His plan so that all forms of life could continue to exist upon the earth.
Then He placed Adam and Eve on the earth. They were different from His other creations because they were His spirit children. In the Garden of Eden, He brought Adam and Eve together in marriage and commanded them to multiply and replenish the earth (see Genesis 1:28). However, their lives were to be governed by moral laws rather than by instinct. — Gospel Principles Chapter 39: The Law of Chastity
That which should be absolutely private is disrobed and acted out center stage. In the shadows backstage are addiction, pornography, perversion, infidelity, abortion, and—the saddest of them all—incest and molestation. In company with them now is a plague of biblical proportion. And all of them are on the increase.
Society excuses itself from responsibility except for teaching the physical process of reproduction to children in school to prevent pregnancy and disease, and providing teenagers with devices which are supposed to protect them from both.
When any effort is made to include values in these courses, basic universal values, not just values of the Church, but of civilization, of society itself, the protest arises, “You are imposing religion upon us, infringing upon our freedom.” — Boyd K. Packer, “Our Moral Environment,” General Conference, April 1992