If I am interpreting religion correctly - you can choose Goddess of Protection (pantheon), that gives a 30% ranged attack bonus to any city following your religion and you can also choose Just War (enhancer) which gives a 20% combat bonus when you are near (2 tiles?) a city that follows your religion.
So as a founder of Absurdism (I like to change the names), for example, and holding the two beliefs above, I would not want to spread my religion to any city I hope to capture at some point, because it would have a 10% bonus against me (30 bonus against me - 20 bonus I have against it).
You could ask - why would anyone combine these two beliefs? Good question. But there is a potential to have conflicting beliefs.
So as a founder of Absurdism (I like to change the names), for example, and holding the two beliefs above, I would not want to spread my religion to any city I hope to capture at some point, because it would have a 10% bonus against me (30 bonus against me - 20 bonus I have against it).
You could ask - why would anyone combine these two beliefs? Good question. But there is a potential to have conflicting beliefs.