Beware of generalising across people you haven't spent much time around, however tempting the hypothesis. Drawing a map of the city from your living room etc.

My first 18 years were spent attending a Catholic church once a week. To the extent that we can ever know what other people actually believe (whatever that means), most of them have genuinely internalised the bits they understand. Like, really.

We can call into question what we mean by 'believe', but I can't agree that a majority of the world population is just cynically going with the flow. Finally, my parish priest is one of the most intelligent people I've ever met, and he believed in his god harder/faster/whatever than I currently believe anything. Scary thought, right?