Even the most staunch believers have "one true religion" and denounce all other religions as false.
That amounts to everyone being atheist to all religions but their own. If we ask people their opinion on all religions and calculate a mean (in colloquial terms people call the mean, "average"), our calculations would reveal that the majority would find all religions as false.
Are there people that believe in all religions, or most religions, or are all religions, or most, mutually exclusive? Or is there a one true religion, and which is it?
The apostle Paul said that there are many gods and many lords, but to us (the early Christian congregation) there was one God, Jehovah and one Lord Christ Jesus.
To every person who adheres to some form of organized religion there is that one true religion, at the least above all. They aren't going to adhere to a false one, are they?
I personally think that there has never been a religion true even unto itself. The ancient Israelite failed miserably even with their God among them, they awaited thousands of years for their messiah and due to religious nonsense they nailed him to a tree when he arrived. The apostle Paul foretold of the apostasy of Christianity within a hundred years of it's founding. And if the Bible had really said Christ would come again, which it doesn't, they would nail him up a second time, I'm sure.
The simple approach to nature and rejection of the worldly ways of the Tao has transmogrified into superstitious priests for hire to bless supermarkets and the Buddha's rejection of the overcomplicated metaphysical and doctrinal complexities of Hinduism has only resulted in surpassing them.
I define religion in its most basic sense, as the strict adherence to a set of beliefs. Everybody is religious. But when an organized religion is divided within the masses it is doomed to fail. For example, when it becomes state recognized. Then again, the state is subject to the same result, isn't it.
Its the System Of Things. Sin.