Of cause this cult is behind sanity and reason, but I didn't see, that they want to impose their believes on others, beside from their normal "advertisement". There is even a Mormon center here in my town. In my time in the bookshop I found loads of their propaganda material in the incoming used merchandise. One time I met even two. I didn't feel a threat coming from them and what they do to their wifes and children is not my business.
They are imposing their beliefs on others in that the children that grow up in these groups are often abused, and forced at young ages to marry, often in an incestuous relationship (like marrying their uncles or cousins). One of the women in the documentary said how her father told her on her birthday one year that she was now one of his sister-wives and he was going to teach her how to please her husband. This is a massive problem in Utah where a lot of girls and women are forced into these types of situations because they grow up in these families and if they leave, they lose everything. They have no job skills, they lose their entire family connection, and there is a big veil of secrecy around it.
One of the people in the documentary talked about how they are programmed, similar to Satanic Ritual Abuse, to keep the secrecy of the group, and that some people would be programmed to kill themselves before they would reveal the secrets.
Most mainstream Mormons aren't like that, but their religion still has cult elements to it even in the milder forms.
The ones in the documentary aren't part of the official Mormon church, but they are a different type of Mormon who are more in line with Mormonism's original teachings. They were kicked out of, or they willingly rejected the main Mormon religion to pursue their belief in plural marriage as the way to their own godhood.