From 19th through 20th centuries the United States was fertile ground for cultivating every imaginable religious sects and here are my five favorite All-American religious cults.
1. Oneida Community
Weirdness Factor: Free Sex
The Oneida Community was founded in New York in 1848. Stripping away all the idealistic rhetoric about perfectionism, it was a sex cult. Their philosophy of Complex Marriage meant that every man is married to every woman and, hence, anyone can have sex with anyone else. Love and pair bonding was discouraged. John and Jane could not just have sex exclusively with each other; the Community would compel them to share the bounty. The Community had special rules (Ascending Fellowship) so the old geezers had exclusive rights to deflower the hot young girls while the geezerettes got the randy teenage boys to themselves.
2. Church of Scientology
Weirdness Factor: It's science fiction
The only religion with a scripture that was first published in a science fiction magazine. The first appearance of L. Ron Hubbard's Dianetics belief was printed in 1950 in Astonishing Science Fiction magazine. Three years later, in 1953, Hubbard founded a religion around it. I'm reluctant to write more because Scientologists have been known to harass people they consider "Suppressive Persons."
3. Church of Jesus Christ of Latter-day Saints (Mormons)
Weirdness Factor: Polygamy
Founded in New York in 1830, everybody knows that polygamy (plural marriage) was a founding article of faith. Mitt Romney's great-grandfather had five wives while founder Joseph Smith had 27 wives and Brigham Young had 51. Unlike the Oneidans, this was a one way deal. Women couldn't have multiple husbands. In 1890 as the price for Utah statehood, the Mormons banned plural marriage, although church members were able to keep any multiple wives they already had. The practice of polygamy continues today within offshoot Mormon sects.
Less well known is Mormonism's inherent racism. Until 1978, the church taught that black skin was the Mark of Cain. Until that date, blacks were considered cursed by God, they were allowed to join the church but were banned from entering the tabernacle. Church teachings still discourage interracial marriages. The Mormon religion is an American-centric religion. It teaches that Jesus came to America after the crucifixion and that the United States is the new Promised Land.
Weirdness Factor: Space Cult
California in general, and San Diego specifically, has been a magnet to space cults. I've known about Unarius since I was young; their headquarters is in the San Diego suburb of El Cajon. Founded in 1954, they believe that extraterrestrials are out there and are friendly, God-like creatures. They come to visit us and, when we die, we go to see them. This is a stable, benign organization.
Certainly the most bizarre space cult was another San Diego product, Heaven's Gate. In 1997, 39 of the tiny cult's members, including its founder, committed suicide so they could join the spaceship that was hiding in the tail of the Hale-Bopp comet.
5. Southern Baptists
Weirdness Factor: Pro-slavery Religion
Before the American Civil War, many religious Northerners had become active abolitionists and were working to end slavery. In the South, the institution of slavery had become a religion. So in 1845, Baptists in the Southern United States split with their Northern brethren solely over the issue of slavery and formed their own church. After the Civil War, the Southern Baptist church became a central base for Ku Klux Klan activities. As the facts around Bob Jones University proves, the 21st century church has not strayed far from its roots.
The University of Virginia has what may be the best compendium of the many different religions and cults in the country.