Religion, of any flavour, is not a theory.
Pinched from Wiki, as that explains it better than my effort: A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment. Such fact-supported theories are not "guesses" but reliable accounts of the real world.
Absolutely none of that applies to religion. It is faith, based upon nothing tangible but (usually) what you told as a little kid. I don't think it's unreasonable to say that the massive majority of people have their faith chosen for them when they are young, as opposed to choosing it for themselves. Bizarrely they quickly discover that neither the Tooth Fairy nor Santa Claus are real, but continue to believe in the presence of an omnipotent being. The irony being of course that both the Tooth Fairy and Santa Claus are very real and very provable, just keep an eye open in the night for when your parents come in!
Would I call someone stupid or thick or choosing to believe? No, I wouldn't. Would I think it? Well, I certainly would struggle to put them at the top of Dan's List Of Smart People, put it that way.
That said, each to their own. Apologies if this link has already been posted, but again it sums it up far better than I ever could.
I understand what makes a scientific theory, a theory as we know it, but the reason it's a theory is because it hasn't been proven or can not be proven, otherwise it would be a scientific law.
Religion/gods etc also can not be proven or disproven and all the "evidence" we have is a very old book made up of many other books/writings.
Anyway, my point is not to support religion, as I don't believe in it myself, but it had it's place in history and making the world what it is today. It's not perfect, but who knows what state we'd be in without it. Changing the education system and beliefs of billions of people doesn't happen overnight and will take several generations to filter out of the mainstream. My only problem is people on their high horses calling those who have faith names and having a superiority complex because they believe they are smarter because they have no faith. It's pathetic really.