I would posit that it's easier to be an atheist in a typical D&D campaign than an agnostic, based on the fact that one could easily say, "These guys aren't really gods, they're just superpowered astral creatures!" It's a lot harder to not know (agnosticism) when one can consult supernatural forces to find out.
That's actually a gnostic, not an athiest. An athiest disbelieves in their existence, a gnostic believes they exist but not as a diety.
And I'd posit neither view is rational in a world where the major troubles of your time directly result from a god dying in a specific spot with specific witnesses who are still very much alive and can be scryed at to see if they are lying.
'So, prove Gods exist.'
'Well, you know how magic stopped working right, and has never worked right since?'
'Yeah?'
'Mystra died.'
'That's superstition.'
'No no, Bob over there's a Chosen of Mystra, and he stopped bein' all Chosen at the same time. He saw it.'
'Everyone's a damn Chosen of Mystra.'
'Not any more. That's a lot of witnesses to the event, don't you think?'
It depends what's involved in ending up in the wall.
I agree that it's very hard to say that "the gods don't exist" in the FR
but it's not entirely unbelievable that a character could believe in the gods but not actually worship any of them specifically.
A wizard could well believe in all the gods but not actually worship Mystra (version IV isn't it now?)
Mystra's dead dead. Like, dead for good dead. There's been no replacement. That's why wizards can't prepare ninth level spells any more, and why anyone can do a ritual.
You can believe in all the gods in FR... and should!... and even give prayers to them from time to time.
Thing is, belief in the gods entails worship. If you believe Aumanator is the god of the sun, then you'd ask for a blessing now and then. It doesn't require a lot of effort, but it does require some action.
If someone 'believes' in the gods but does not actually do anything to make them relevant, then no god's proxy is going to come for him in the fugue plane because he's done nothing to get their attention. That's the bit that gets you on the wall. If you have the attention of many gods, well, that's not so bad.
The reason people get stuck up on the wall isn't some spiteful 'Hey, you sucked at this whole worshiping gods on Toril thing.' It that all the dead go to the Fugue Plane, and they wait for the proxies of a god to come by and get them out of there. If they're not picked up, because they didn't bother to get noticed through a sincere prayer now and then... well... up on the wall they go.
'But isn't atheism a choice!?!"
Actually, Kelemvor believed that. When he started off as the God of the Dead, he let the good side of him prevail. He wouldn't stick people up on that wall.
The problem with that is that the forces of Toril ARE run by the gods. The sun moves -because- of Aumanator. Magic -works- because of Auril. Hate and strife are -fed- by Bane. The gods are actually there for a purpose set down by Lord Ao. If there's no punishment for disbelief, and people can actually learn that, then why believe? Everything will work as it should right?
Except it won't. The portfolios of the gods MUST exist. The gods require worship to power their abilities, and their abilities are required to keep their portfolios in line. Individual gods can die, be born, take over other portfolios, or have mortals ascend to their status. But the
portfolios must be maintained. And if something constitutes a long-term threat to the gods' portfolios, that actually means a long term threat to the stability of the universe itself.
Look at what happens when
one portfolio goes kaput? Spellplague. The Weave unravels. Universes collide.
There are people who'd be defiant, and would say 'Gods don't exist!' But once it can be proven they do exist, and that atheism is 'rewarded' with eternal damnation... well... there's actually not a lot of people left who would qualify for the wall. That leaves madmen... who Cyric can take anyways... and those who pretty much deserve it for being stupider than those who go to church because 'it's what momma says we do.'
Eventually Kelemvor relented because he realized there's a natural order to the universe in the Realms, and that every thing in the outer planes has a reason and a place, and his place involved properly administering the dead. It meant not denying the evil gods their petitioners just because he did not like them. It meant not saving nonbelievers from the wall, because it
was causing problems in the world, even that short time. Mystra was forced by Lord Ao to grant Cyric's clerics access to the Weave, Kelemvor was forced to stick the lost onto the wall. It was necessary to keep the world working.
Being a god on Toril isn't about being sympathetic to the causes of your followers, it's about embodying the essence of your portfolios, keeping that crap running as it should, and the followers being sympathetic to YOU.
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Now on Eberron, belief, faith, and worship aren't even necessary to gain power from your diety, nor is a diety even necessary. You could be a heretic of your church, or even worse, you could 'worship' the lawful good Silver Flame, but actually be a chaotic evil servant of the demon she locked away serving as a member of the clergy. And if you were a divine powered character, you'd get your divine power just as if you were the most noble of paladins. Atheism IS a valid choice in Eberron, as the gods are distant and simply do not involve themselves that closely. Divine power comes from something else.
