That statement is an oversimplification, especially since the RLDS came to believe on good evidence that Joseph Smith Jr was not a polygamist. Back when they were contending against polygamy, RLDS ministers liked to quote Jeremiah 17:5-8, reading into it as follows:
"Thus saith the Lord; Cursed be the man that trusteth in man, and maketh flesh his arm, and whose heart departeth from the Lord [Brigham Young]. For he shall be like the heath in the desert, and shall not see when good cometh [the Reorganization]; but shall inhabit the parched places in the wilderness [beyond the reach of American law], in a salt land and not inhabited [Salt Lake City and surroundings]. Blessed is the man that trusteth in the Lord, and whose hope the Lord is. For he shall be as a tree planted by the waters, and that spreadeth out her roots by the [Missouri] river, and shall not see when the heat cometh, but her leaf shall be green; and shall not be careful in the year of drought, neither shall cease from yielding fruit."
God loves repentance. No matter what the sins of the Mormon church were, that church is doing much more good than evil now. "Let the wicked forsake his way, and the unrighteous man his thoughts: and let him return unto the Lord, and He will have mercy upon him; and to our God, for He will abundantly pardon. For My thoughts are not your thoughts, neither are your ways My ways, saith the Lord. For as the heavens are higher than the earth, so are My ways higher than your ways, and My thoughts than your thoughts" (Isaiah 55:7-9).
No simplification involved - it is a statement of fact. Additionally -
June 7, 1844 -- William Law, 2nd counselor in the 1st presidency, leaves the church over polygamy and Joseph's denial of it. Soon thereafter, he publishes the 1st and only edition of the Nauvoo Expositor, which claims 1st-hand testimony from several sources that Joseph was practicing polygamy, counter to his public denials. This was NOT an individual attempting to justify their "sin" John. As such is not one of your 'tainted' sources'.
In 1838,Oliver Cowdery is excommunicated, at least in part, for accusing Joseph Smith of adultery with Fanny Alger. He was NOT trying to justify his sins John
D&C 132 was written while emma was still alive - you may argue exactly when, but it states "52 And let mine handmaid, Emma Smith, areceive all those that have been given unto my servant Joseph, and who are virtuous and pure before me; and those who are not pure, and have said they were pure, shall be destroyed, saith the Lord God." I believe that the use of the PAST TENSE here makes it clear.