I don't think celibacy of priests is a good example of this. For one thing, it rarely actually happens, as priests routinely abdicate in order to marry or just

I don't think celibacy of priests is a good example of this. For one thing, it rarely actually happens, as priests routinely abdicate in order to marry or just father children out of wedlock. For another, if only priests are celibate but everyone else is forbidden from using birth control, numbers will always outweigh the cost of the celibate priests. Even suicide bombers can, through their zeal and dedication, inspire many others and bring groups and clans closer. Heaven's Gate though, you can't really argue a net positive for, since they're all gone. Certain religions are more successful than others for the same reason that other organisms are more successful: they adapt more quickly to their environment.