The reason religion is so powerful

[Abaddon_ire]

I suppose to test this, we'd have to work out whether people have been more or less willing to do violence for political purposes than for religious purposes. 

Nope. Such a test would be morally abhorrent. Yet we have seen such tests in real life. It is not some intellectual exercise, something you seem to believe everything reduces to. No, not at all. In reality, millions have died on foot of such philosophical babblings.

Your problem is that you are stuck in academic philosophy. All clean and pretty.

You really do not care about what people do with that afterwards. The practical results of your navel gazing are unimportant to you.