Zendaze, do you ask if those millions who believe in a mad religion must necessarily be mad?
No, I don't think they are. People compartmentalise ideas, including religious concepts; they rarely analyse them.
A few, no doubt, are religious nutters. I have met a few over the years, so I have no doubt they exist. But for most people who claim to be religious, they wear it like a coat; they put it on as occasion demands, and remove it also, without ever thinking about how it was made, or examining the quality of the seams which hold it together. Those who wish to learn more about their own religion usually have prescribed books to read, which will reinforce what they have learned already, thus keeping them on the strait and narrow path.