No, that is not true.
After 1852, when the Mormon Church was openly practicing polygamy, the leaders of the church were declaring that it was absolutely essential for exaltation. **Joseph F. Smith, who **
served as the 6th president of the church, made this emphatic declaration concerning the importance of polygamy:
** "Some people have supposed that the doctrine of plural marriage was a sort of superfluity, or non-essential to the salvation of mankind. In other words, some of the Saints have said, and believe that a man with one wife, sealed to him by the authority of the Priesthood for time and eternity, will receive an exaltation as great and glorious, if he is faithful, as he possibly could with more than one. I want here to enter my protest against this idea, for I know it is false.
… Therefore, whoever has imagined that he could obtain the fullness of the blessings pertaining to this celestial law, by complying with only a portion of its conditions, has deceived himself. He cannot do it. When that principle was revealed to the Prophet Joseph Smith,… he did not falter, although it was not until an angel of God, with a drawn sword, stood before him and commanded that he should enter into the practice of that principle, or he should be utterly destroyed, or rejected…**
Code:
"If then, this principle was of such great importance that the Prophet himself was threatened with destruction,... it is useless to tell me that there is no blessing attached to obedience to the law,** or that a man with only one wife can obtain as great a reward, glory or kingdom as he can with more than one,...**
"I understand the law of celestial marriage to mean that every man in this Church, who has the ability to obey and practice it in righteousness and will not, shall be damned, I say I understand it to mean this and nothing less, and I testify in the name of Jesus that it does mean that." (Journal of Discourses, vol. 20, p. 28-31)
In 1891 the First Presidency and Apostles of the Mormon Church made the following statement in a petition to the President of the United States: "We formerly taught to our people that polygamy or celestial marriage as commanded by God through Joseph Smith was right; **that it was a necessity to man's highest exaltation in the life to come.**" (Reed Smoot Case, vol. 1, page 18)
Apostle Orson Pratt strongly affirmed that it was absolutely essential that polygamy not be given up by the church:
"**God has told us Latter-day Saints that we shall be condemned if we do not enter into that principle; **and yet I have heard now and then... a brother or sister say, 'I am a Latter-day Saint, but I do not believe in polygamy! Oh, what an absurd expression! What an absurd idea! A person might as well say, 'I am a follower of the Lord Jesus Christ, but I do not believe in him.' One is just as consistent as the other.... If the doctrine of polygamy, as revealed to the Latter-day Saints, is not true, I would not give a fig for all your other revelations that came through Joseph Smith the Prophet; I would renounce the whole of them, because it is utterly impossible.... to believe a part of them to be divine — from God — and a part of them to be from the devil;... The Lord has said that those who reject this principle reject their salvation, they shall be damned, saith the Lord;...
"Now I want to prophecy a little.... **I want to prophecy that all men who oppose the revelation which God has given in relation to polygamy will find themselves in darkness;** the Spirit of God will withdraw from them the very moment of their opposition to that principle, until they will finally go down to hell and be damned, if they do not repent.... if you do not become as dark as midnight there is no truth in Mormonism." (Journal of Discourses, vol. 17, p. 224-225)