Star Cults existed in the Starless World, an alternate version of Earth that came into existence at the edge of total event collapse, after every star in history had been erased, leaving Earth and its moon as the only planetary bodies in the entire universe. (TV: The Big Bang)
History
According to a brief conversation between Amelia Pond's aunt Sharon and a psychiatrist, Christine, people seeing or believing in stars was common throughout history.
Sharon expressed worries that Amy would grow up and join a Star Cult and said that she didn't "trust that Richard Dawkins". (TV: The Big Bang)