I think purity and lack of purity are both required for a religion to be a successful meme. To much purity and the religion faces a "no true scotsman" decline

I think purity and lack of purity are both required for a religion to be a successful meme. To much purity and the religion faces a "no true scotsman" decline resulting in schisms and deconversion To little, and it becomes too diluted to hold any significance. The way a religious macromeme manages the level of purity in an evolving social environment is natural selection at work.