Some of them are close to being orthodox Christian; the "Community of Christ" (formerly the Reorganized CoJCoLDS) is Trinitarian, for example.
Correct. Some split off while Joseph Smith, Jr. was still alive because they found out he was committing polygamy and polyandry (marrying other men's wives) and lying about it. One of them was started by William Law after Joseph Smith, Jr. asked Law's wife to Celestialize with him (that's have sex with him, for those of you from Tuscaloosa).
When she refused to become Smith's 40-oddth wife, the LDS powers started a rumor that she was having an affair. And then when Law objected, Smith did two things. He gave a famous sermon in which he declared that he had been accused of having multiple wives but he could only find one. And he made certain William Law was excommunicated.
Less than a month later, Law has started a spin-off that taught the Book of Mormon was truth, but that Joseph Smith was a fallen prophet (the BOM taught that polygamy was a sin). Law was one of the editors of the Nauvoo Expositor, which published a single edition that, among other things, exposed Smith as a polygamist.
Smith ordered the printing press destroyed.
Yada, yada, yada. Smith declares martial law. Treason charges. Carthage jail. Smuggled guns. Smith shoots and kills a couple of men. Smith dies primarily because he's been practicing polygamy since 1831 and lying about it publicly. And he's taking the wives of other men as his wifes. And he's propositioning the wives of other men, and they turn him down. And he excommunicates a man who announces it publicly. And he orders the destruction of a printing press that prints the news that he's a polygamist.
Even in this day and time, messing around with and sleeping with other men's wives will get you killed. Lying about adultery isn't a good idea.
It certainly didn't work for Joseph Smith.
A few of the sects broke off from the Brighamite branch of the church and stopped practicing polygamy as well.