This is a controversial topic, but it is useful to give it some thought.
Let us not confuse Faith with Religion and God in our debate.
If you observe the general trend, the more the affluent and secure a society is, the lesser the belief in God and following a religion.
There are 2 possibilities in being non-religious.
One is an extreme step taken by a country like China to ban religion OR something that is voluntary and personal.
If you look at Scandinavian countries, people are no so religious there. And observers conclude that this is since the people are secure there.
They do not feel the need to depend on something that might “help” to improve their condition.
I agree with that hypothesis.
(image courtesy Wikipedia)
If you observe poorer countries, they have a strong religious sentiment.
Look at the Middle-East, and look at how the extremists and terrorists take advantage of poverty and ignorance to add to their numbers.
As a society becomes richer and stable, it becomes more economically secure and this leads to more personal security and it will become less religious.
This article – http://www.huffingtonpost.com/nigel-barber/why-americans-are-more-re_b_814962.html – says it better than I can.