There has never been a case where a person has returned from the dead. Also, the dead do not communicate with the living, not ever. Nor have the dead provided any evidence that they continue to think or act. There is nothing to fear in the dark, no mystery surrounding death, no supernatural creatures lurking in cemetaries or morgues, and no ghosts from the past. Morticians do not work in fear that the corpses might suddenly spring to life again.
Grave diggers hear no whispers from the ghosts of bodies buried in cemetaries.
Soldiers in battle have nothing to fear from the corpses around them and are not avenged by the spirits of those they have slain. Machiavellian leaders have every reason to encourage a belief in the afterlife and to encourage religion itself. A system of thought where questioning is forbidden strengthens the power of a dictator, while harming a democracy. Religion casts an opiate haze over the eyes of the people, making them passive and easily used for whatever purpose is at hand, be it war or exploitation at the hands of the wealthy owners. Without a culture that nourishes a healthy skepticism, the ruling class may act without scrutiny.