Latter-day Saints who go through temple rites covenant and promise before God, angels and witnesses to obey the law of chastity; which is that they will have no sexual intercourse except with their spouse to whom they are legally and lawfully married.
In Illinois during the entire 1840s it was illegal to be married to more than a single spouse. In the United States Territories it was likewise a crime to be married to more than one spouse. Because of open, unlawful cohabitation by members of the LDS church beginning in the early 1850s, Congress enacted harsher and harsher penalties to stop that unlawful conduct. Congress ultimately confiscated LDS church property to compel them to obey the law. Apparently the LDS church valued property more than their religion because they abandoned unlawful polygamous marriage as a tenet of their faith.
Because no LDS marriage was lawful except with the first wife, all LDS and Fundamentalist LDS men who took plural wives and had sexual intercourse with them from the 1840s through the present, have violated the law of chastity. They have been and are adulterers.
For this reason I have denounced polygamy and advocated ending the practice of taking multiple wives. Those who violate the law of chastity will be condemned by the commandments of God. Those who took temple covenants violated their commitment before God, angels and witnesses by having sexual intercourse with women to whom they were not legally and lawfully married. According to the Book of Mormon they will be thrust down to hell. (2 Ne. 9:34, 36.)
Joseph Smith appears likely to have sealed other women to himself. But there is scant proof he treated them as wives and had sexual intercourse with any of them. He fathered children only with Emma Smith, his legal and lawful wife. Others were apparently sealed to him only to bind them into an eternal relationship. That sealing would allow him to take them with him into the Celestial Kingdom as part of his extended family.