The world can provide for growing population. Many people, some of them innocently caught up in the whirlpool of delusion errors, are worrying about the earth failing to provide for the oncoming generations. They take such means to influence the thinking of the people and repeat it so often that many of us were gullible and accepted it. We tend to believe what the world says. We often do not even ask what the Lord’s program is. 
Ezra Taft Benson
The precepts of men would have you believe that by limiting the population of the world, we can have peace and plenty. That is the doctrine of the devil. Small numbers do not insure peace; only righteousness does. After all, there were only a handful of men on the earth when Cain interrupted the peace of Adam’s household by slaying Abel. On the other hand, the whole city of Enoch was peaceful; and it was taken into heaven because it was made up of righteous people.
And so far as limiting the population in order to provide plenty is concerned, the Lord answered that falsehood in the Doctrine and Covenants when he said: “For the earth is full, and there is enough and to spare; yea, I prepared all things, and have given unto the children of men to be agents unto themselves.” 
A major reason why there is famine in some parts of the world is because evil men have used the vehicle of government to abridge the freedom that men need to produce abundantly. True to form, many of the people who desire to frustrate, through worldwide birth control, God’s purposes of giving mortal tabernacles to his spirit children are the very same people who support the kinds of government that perpetuate famine. They advocate an evil to cure the results of the wickedness they support. 
John A. Widtsoe
Not the least of the evils resulting from birth control is the failure to maintain the population of the land. The birthrate in the United States is on a steady decline. Per thousand of population it has fallen from 25 in 1915 to 17 in 1939, and appears to be still declining. In 1941 the reproduction rate in the United States was below the death rate. Such a condition weakens the race. The nations that will possess power in the future, will be those who maintain a normal birthrate.
The Latter-day Saints, true to their teachings, have maintained a high birthrate, at present nearly twice that of the United States. Children continue to be welcomed in Mormon households. 
↑ Spencer W. Kimball, Teachings of Spencer W. Kimball, p. 331