Celebrim
Legend
One option could be to pick some real-world religions, replace all real-world names and terms, and then modify the details here and there.
I think it isn't a bad idea to inform your world's religions with your knowledge of real-world religions, but I think it is a serious mistake on several levels to mix real-world religions with the serial numbers filed off or in pastiche or really in any other form with the game. An invented pantheon is better in every way, and less likely to cause table conflict.
The difficulty in representing a more realistic take on religions, is that belief is also added, but eventually there is disagreement at every possible level, even at the level at which some pretend they don't believe but rather know, while others that it is impossible to know.
This is no real difficulty. Have the gods themselves advocate for these very positions. One god insists he doesn't just believe that his way is right, he knows it is. Another god scoffs, not only are you wrong, but it is impossible to know anything. "Truth is just self-delusion; there is no truth except that there is no Truth.", claims the chaotic god.
This means, that real-world religions have a lot of overlapping: for instance all monotheistic religions essentially believe in Good, but clearly they often have heated discussions to say the least.
Monotheistic religions quibble over the will, nature, and desires of their deity. But this isn't an exclusively monotheistic problem, and imagine the heated discussions that occur in a polytheistic setting when you have say 4 or 5 different deities vying for dominion of the province of rain and weather - each claiming the right to priority of worship, primacy of their moral outlook, first place in offerings and services, and superiority by just right over their fellows.
All in all I'd say that you'll have to tread carefully between making religious powers tangible, and not being able to reveal much about which religion is true if any.
Having all religions be 'true' in the since that some powerful being representing the object of the worship of that religion exists, in no way at all reduces the conflict between them. The essential question of, "What do you choose to believe?", or may be more to the point, "What one ought to believe?", remains.
Yes. I suppose you can actually DM a religion-fiction campaign (think The Da Vinci Code) to be a success. Although IMO that kind of story works well if it's based on actually the real world, i.e. if you have the characters live in our world, and discover some uncomfortable truths about real-world religions.
This is I think incredibly naïve. For example, suppose your group is mostly atheists and you play an Indiana Jones type campaign, and you discover the Ark of the Covenant and that God Is Real. Does this constitute an uncomfortable truth to your group? No, of course not. The atheists are likely to believe simply, "For the purposes of the campaign, this is true." But now suppose the Storyteller insists, "No, you guys aren't getting it. We are playing in the real world. God really exists." Again, does this constitute an uncomfortable truth? No, again, this constitutes an uncomfortable moment at the table, where in the atheists in the group learn the story teller can't separate the fiction of his story from reality, and is busy proselytizing behind the DM screen, but it's not like the atheists have never encountered fiction that presumes the existence of God.
Now reverse the situation. Suppose your group is mostly believing orthodox religious and you decide to do a Dan Brown style game where various heresies are revealed to have a basis in fact. Does this represent an uncomfortable truth? No, of course not. The believers in the group will simply accept that for the purposes of this fiction, those things are true but they have no bearing on the real world. It's not like believers have never encountered stories in which various heresies are presumed to be true, or fiction in which God is presumed not to exist. If the Story Teller insists, "No, you aren't getting it. We are playing in the real world. God isn't real.", will this be an uncomfortable truth? No, but it likely will be an uncomfortable moment at the game table, as the players realize that the story teller is unable to separate his conceits from reality and that he's trying to proselytizing from behind the DM screen.
At best either way you'll end up with an argument over whether or not the story teller has his facts straight and an outbreak of, depending on the zeal of the parties involved, passionate attempts to covert people over to their way of thinking. No one of which makes for much accomplished within the gaming session.
Now, I suppose you could have a reasonably successful campaign presenting the players with comfortable validation truths - a campaign that preached to the choir, as it where. If the group was entirely believers, a story line that validated that the fantasy world had the same God as the real world might be validating, comfortable, and welcome. Likewise, among a group of non-believers, a story line that validated non-belief and presented the proxies of believers of the real world in an unflattering life might be similarly validating, comfortable, and welcome. But this is hardly the same as exploring religious or moral space in your game play, and chances are you'll find your players beliefs aren't nearly as uniform and predictable as you might have presumed.
I've been friends with Atheists, Christians and Hindus. I've gamed with lapsed Moslems and lapsed Mormons, but also believing Mormons and believing Evangelical Christians. It's alright to have players with different opinions giving their different opinions through their play. But its best to keep this all as a proxy friendly discussion, and not try to impose your views as DM on the players by asserting things about the player's real beliefs through your claims in game.
If you make them exist in a totally fantasy world with totally fantasy religions, chances are they couldn't care less for fantasy deities to be proved false or different.
Yes, but in a fantasy story fantasy deities can in fact be proved false or different. A fantasy story can prove nothing about a deity presumed to exist (or not exist) in the real world.
GK Chesterton once said, "A good novel tells us the truth about its hero; but a bad novel tells us the truth about its author." If you have fantasy gods, you leave space for the reader learn something unique about the people in your fantasy world. If you have a pastiche of real religions, you only end up telling us what you believe.