It depends what kind of religion you mean. A believer who identifies god merely as a kind of 'prime mover' for the universe who doesn't intervene/answer prayers/talk to prophets and politicians is, to all intents and purposes, virtually indistinguishable from an atheist - especially from the perspective of rationality or the advancement of the human species.
Any believer, however, who identifies their god/s as an interventionist, all-powerful and innately moral director of the cosmos, will be in for more problems. Why? Because this is god that it is virtually impossible to reconcile with anything we observe about the world or the universe in a way that is rational. Hence why in recent times, better-read believers have begun turning to various traditions of mysticism to explain their deity - which is almost by definition anti-rational.