When people get together to talk about religion, too often the word "cult" is tossed around as a pejorative to mean any religious movement they don't like. Never mind that Catholicism has been around for 2,000 years and has over 1 billion adherents, it's called a cult by people whose own particular religion was started in 1984 and might claim a total of 75 adherents. What is sorely lacking is an objective standard by which we can identify something as a cult.
The crucial moment for any new religious movement is the death of its founder. If the movement was centered around one strong figure merely to allow him to exercise power over the men and get sexual favors from the women, then it most likely will shatter upon that leader's death. If there is at least a core of truth in the movement, it will survive the death of its leader, such as the lynching of Mormon founder Joseph Smith, and perhaps rally around another one, such as Brigham Young, who led an LDS remnant from Missouri to Utah.
So we can define a cult as simply any new religious movement whose founder has not died. And by death, we're not talking about those close calls in the operating room where the heart stops for a few moments, we're talking about someone who is whipped to within an inch of His life, nailed to a cross all day, then buried in the ground over the weekend. So right away, historical Christianity is not a cult because Christ has died.
Overcomer Ministries in South Carolina, however, is a cult because founder R.G. Stair has not died (going to jail doesn't count). Jehovah Witnesses are not a cult because Charles Taze Russell, who founded the movement in 1877, died long ago. Calvary Chapel is a cult because Pope Chuck Smith has not died, but the Worldwide Church of God is not a cult because Herbert W. Armstrong has died.
