I among others out there believe that LDS D&C 132 the polygamy section was not revelation from God through Joseph Smith.

One key that Joseph Smith taught in regards of knowing if a revelation came from God or not is whether or not it contradicts previous revelation from God or not.

How it may be asked was this known to be a bad angel? … by his contradicting a former revelation. – Joseph Smith, Times and Seasons 3, April 1, 1842

Lets first read 2 Nephi 28:8 and LDS D&C 132:26, the added emphasis is mine.

2 Nephi 28:8 And there shall also be many which shall say: Eat, drink, and be merry; nevertheless, fear God—HE WILL JUSTIFY IN COMMITTING A LITTLE SIN; yea, lie a little, take the advantage of one because of his words, dig a pit for thy neighbor; there is no harm in this; and do all these things, for tomorrow we die; and IF IT SO BE THAT WE ARE GUILTY, GOD WILL BEAT US WITH A FEW STRIPES, AND AT LAST WE SHALL BE SAVED IN THE KINGDOM OF GOD.

LDS D&C 132:26 Verily, verily, I say unto you, if a man marry a wife according to my word, and they are sealed by the Holy Spirit of promise, according to mine appointment, and HE OR SHE SHALL COMMIT ANY SIN OR TRANSGRESSION of the new and everlasting covenant whatever, and all manner of blasphemies, and if they commit no murder wherein they shed innocent blood, YET THEY SHALL COME FORTH IN THE FIRST RESURRECTION, AND ENTER INTO THEIR EXALTATION; but they shall be destroyed in the flesh, AND SHALL BE DELIVERED UNTO THE BUFFETINGS OF SATAN UNTO THE DAY OF REDEMPTION, saith the Lord God.

Just to make sure we are on the same page, 2 Nephi 28:8 is a verse where Nephi is describing what vain and foolish people will teach others. To put it simply, these are not things we want to copy or follow after. To confirm this lets look at the next verse.

2 Nephi 28:9 Yea, and there shall be many which shall teach after this manner, false and vain and foolish doctrines, and shall be puffed up in their hearts, and shall seek deep to hide their counsels from the Lord; and their works shall be in the dark.

LDS D&C 132 is a copy of a revelation that was supposedly received by Joseph Smith regarding polygamy found in a desk years after Joseph Smith was murdered and it had to be a copy because Emma had burned the original.

In 2 Nephi 28:8 Nephi is telling us that people will foolishly teach that it will be okay to sin because God will just beat us with a few stripes and then we can go to Heaven. In LDS D&C 132:26 who ever the author is of this verse is telling us that same idea but is saying it is a true principle if we have been married by the Holy Spirit of promise. 2 Nephi 28:8 and LDS D&C 132:26 are in conflict with each other. In fact I would say 2 Nephi 28:8 is a prophecy how people would teach foolish doctrines that LDS D&C 132:26 contains.