There is a small group of people who, when confronted with the constant excesses of modern society, combined with insurmountable problems in the workplace or home, decide to sell all of their possessions, shave their heads, and join a doomsday cult. These apocalyptic groups believe that the end of the world is nigh (it’s possible), and that they possess the sole means towards salvation (not quite as likely). There’s also usually a forbidden barn in there somewhere and a widely held perception that “The Leader” needs to have as many wives as possible.
One of the more dangerous aspects of a doomsday cult is their willingness to kill themselves, or others, in the name of the group. If the world is about to be invaded by flying saucers from the Horsehoe Nebula, then there really isn’t much reason to hold oneself back (especially if the aliens are able to reconstitute their bodies.) You thus end up with situations like Heaven’s Gate, who were convinced that mass suicide would allow them to hitch a ride with a spaceship carrying Jesus that was hidden behind the tail of the approaching Hale-Bopp comet. Sadly, he chose to take a later flight, so their sacrifice was for naught.