Whilst I am still undecided about Heaven, I do believe in souls. Everyone has something unique about them and that doesn't have to be linked to a deity. Besides, if souls aren't real, then The Prisoner of Azkaban would just be a story about an escaped murderer who got snogged by a hooded demon. And then where would we be?
One ought always to be on one's guard about those who assert that to think in a certain way is to commit a sin. This is the immoral and bullying trick that religion plays. Couched in cosy rhetoric and increasingly vague threats is the assumption that, in dissenting, you are subjecting yourself to an eternity of howling pain and misery.