The leaders of the groups have one central goal, and that is to gain complete control over the people in their cult, regardless of the ramification. Many times this includes forced sexual encounters, withholding of food, and other extreme measures. Frequently the leader, usually male, will gain such control that he will convince his followers to commit crimes, such as suicide or murder. Often times these groups appear or claim to be religious, as a way to sway possible followers.
The biggest questions are about how the control is obtained and how it is possible for these people to be swayed so easily. A lot of times these "leaders" focus their persuasion on those who are most vulnerable. Many of these leaders will not release information about their tactics; that is if they are alive, as many have died during ritual suicides and mass murders.
These mentally disturbed people who are the founders of these groups focus all of their power on psychologically controlling vulnerable people who they can easily manipulate. As previously stated, they can sometimes make erroneous claims with no substantial data. This is why these groups are often based on some type of religion.