I feel like I should point out that the official Church of Jesus Christ of Latter Day Saints has officially repudiated polygamy (except insofar as men can be "sealed" to several wives if it happens that each dies before he marries the next). I've lived in Utah and this repudiation is carried out in everyday social stigma; it's not just on paper. Since "Mormon" is recognized as a nickname for that religion more readily than its spinoffs, calling polygamist sects "Mormon" instead of the distinct "Mormon fundamentalism" is misleading and perpetuates stereotypes. "Fringe" is a nod to this, but it doesn't specify what it's on the fringe of (even standard-issue Mormonism could be considered on the fringe of, say, generic Christianity).