I think I read you wrong initially. You're not saying religions do this, rather there are groups who pretend to be religions that do this.
And you're correct about that. Religions tend to have a very specific set of rules and that's it. So there's no spiral, rather there is a specific level to get to and no further.
But these other groups do tend to spiral. However they also tend to burn themselves out quite quickly.
It's one of the ways of distinguishing a religion from a cult.
Not as much as you would think. In particular, religious groups that enter really tight spirals tend to blow themselves out. I'd say religions are successful in spite of their purity spirals rather than because of them.
