The idea that humans have an immortal soul is a deceptively deadly idea for humans.
The only people who would fight in wars would be mercenaries. There is no way you could get people to die if they thought that was it.
Belief in an imortal soul makes people callous to starvation and suffering. After all - this life is just a brief sojourn in the earthly school of misery.
And why take care of the planet? We're all going to leave it anyhow. And if you leave it in a mess people will be able to suffer and die sooner and get on to the next world.
If we are souls occupying feeble fleshly bodies then the Heavens Gate sect had it right. Shed your miserable body as quick as you can. The greatest favor you could do anyone is to liberate them from this flesh-burdened existence.
I like the concept of spooky imortality. You know - where you can hang around invisible as a ghost and get even with your enemies or maybe take on the role of incubus.