"To join a cult" means to become part of a group or organization that has extreme or unconventional beliefs, often led by a single leader. It usually involves following strict rules and surrendering personal autonomy to the leader. Full definition
Though only 6 percent of the population is diagnosable, powerful societal influences are tempting the rest of us to join the cult of self. (entrepreneur.com)
the pope's sister didn't want him to be pope because she knows when people join cults, like christianity, they often leave their loved ones and have delusions of grandeur, like that they can directly speak to deities. (religion.blogs.cnn.com)