What is the difference between a cult, Christianity, and Islam?
The number of followers.
The less followers, the more whacky/unique it’s able to be.
One could describe it as the natural selection of belief systems. Successful belief systems spread, survive, and get transmitted to the next generation.
Over centuries, they withstand environmental changes through adaptation (E.g. various Christian branches accepting evolution) or in the absence of adaptation, by resisting those environmental changes (E.g. faith enforceable by law in Saudi Arabia).
The adaptability of each branch in the belief evolution tree determines the degree of whackiness perceived by everyone outside your evolutionary branch.
It’s basic science. The only question is who created the first belief system?