In many ways, this is the big question of belief. Not the existence of God or gods, but the existence of the afterlife strikes me as harder to prove or disprove. After all, Zeus Panhellenios could manifest tomorrow and that would prove something – but the undiscovered country is going to remain undiscovered until after death.
So it comes down to gut instinct, really. There’s no real way, so far as I can tell, to prove or disprove the existence of any afterlife from this side of the grave. But that doesn’t mean that the idea of it can’t inform moral judgements.
My opposition to the death penalty, for example, is partially based on not being able to tell whether this life is all we have or not. If it is, then there could be few things as immoral as killing as a punishment – particularly given the possibility of wrongful convictions. (If there is an afterlife, I would still potentially have moral issues with it, because my standards of justice differ dramatically from those of the medieval and pre-medieval minds that devised all these afterlives.)
The conditions for entry to various afterlives that I am aware of are all, without exception, restrictive and discriminatory – not that that’s all bad. Many of them seem to act as a filtering system for people I would prefer not to spend eternity with (Valhalla springs to mind, as does wherever suicide bombers think they’re going to go and those particular Heavens favoured by some born-again Christian sects in which getting to watch other people being tortured in Hell is part of the attraction). But the arbitrary nature of the restrictions, coupled with the punitive conditions most afterlife systems impose on those who don’t qualify, really, really disturb me – and in many cases, act as an encouragement to behaviour I consider immoral in this world.
Moreover, if the afterlife that existed were to be the of the kind depicted in many modern religions, it would actually make a mockery of the beliefs in question. Because the whole presummption of so many faithful that religion is required for morality is a flawed idea in any case, resting as it does on the idea that it is somehow more moral to behave in a decent fashion in the hope of receiveing a future bribe than just because it’s the right thing to do. For that very reason, I find myself hoping that there isn’t such an afterlife.