Heretic of The Seventh Circle
Or without the wall but with gods, like every other dnd setting.The Gods are obviously real, they're obviously super powerful, and they make no bones about being in charge of what happens to you after you die. If the Gods are remotely like people, you can imagine they wouldn't look to kindly on mortal souls who deny them. Being an atheist or agnostic in D&D is nothing like in real life.
Worse, loose souls are the equivalent of barrels of gunpowder laying around. Devils use them as tank-fuel (not to mention just plain warping souls into devils), etc. So you could think of the wall as a toxic waste disposal system. If you're a big jerk like Myrkul, you'd render some punishment (again, mortals know this wall exists!) If you're Kelemvor, maybe I don't see Kelemvor letting this be so awful. But it is up to the God of death who gets the first crack at these souls. And generally the god of Death isn't interested in letting a big stream of unclaimed soul-power getting lose.
If I recall right, part of the (4E?) Raven Queen's issue was fending off planar soul thieves for just this sort of reason.
It makes a certain internal sense at least. If you want to say the D&D authors are being mean to RL people who are atheists and agnostics, well... they can play D&D without gods and the wall.
The wall makes the gods Evil. Full stop.
Edit: like...a person who doesn’t care about the gods, would count as faithless. Also, so what if some guy believes the “gods” are just powerful people who found a path to immortality and extreme power? Literally so what? The idea of it being appealing to have divine retribution for such a thing is...disturbing.