The word you are looking for is cult.
10 warning signs of a Cult
Why People Join Cults:
To those on the outside, it can be difficult to understand why anyone would join a cult.
They Don't Know They're Joining a Cult - Most individuals don’t recognize the group they’re joining is considered a cult.
They Have Unresolved Insecurities
Another study found that many cult members experience attachment insecurity prior to joining a cult. Their insecurities may drive them toward a group that promises acceptance.
Once they join a group, they’re usually distanced from outside influences. After people are separated from the outside world, leaving the group becomes difficult. They often grow dependent on being in the group and develop suspicions of anyone outside the group.
This is why some people suspect that cult members are “brainwashed.” And there is some science behind this idea, as members are often told they’re being persecuted by people outside the group.
They Are Manipulated Into Joining
The other major theory about why individuals remain in cults is mostly sociological. Cult leaders often promise to reward members in some way. They may tell them they’re going to move up the ranks within the cult or they may convince them that something really good is going to happen to their special group.
Does all that sound familiar? Yes, those on the outside can't understand. It's weird because it's a fucking CULT!