if we are a regular organism like every other regular organism, we shouldnt even have such desire
You refer to the innate behavior of humans (memorialising the dead, for example) in your argument for an afterlife, then claim we don't operate on instinct. Any innate behavior is an instinct, pretty much by definition.
That one of our instincts is to learn and grow, explore ideas and discover truths doesn't really mean anything. Our nature is still built on instinct. Besides, plenty of other creatures learn about their environment and have complex social structures which are constantly changing over time to incorporate new ideas (these are not simply instinctive in the same way as a spider building a web is).
Our human nature - curious, moralistic, compassionate, intelligent, logical, social, loyal, not to mention being fascinated with spiritual, moral and philisophical questions, has served us well throughout our history. Civilisations have been built, united and maintained on the basis of these human traits and on these ideas.
It's not difficult, surely, to see how these tendencies may have been of an evolutionary advantage to modern humans.
You either have to accept that there is a good basis by which our nature could have given us evolutionary advantages or you have to admit that these traits don't actually do us any good, in which case, why do you praise them so highly?
As an additional point, it's worth noting that elephants have been well documented as memorialising their dead (look it up. I'm serious.). Chimpanzees have also been seen to display signs of grief and anguish towards death, which may not be 'memorialising' but even if it isn't, it's certainly not a long way off, in evolutionary terms, for that behavior to take the form of long term grief.
The longer and more intense the grief, as we all know to be the trade off in life, the more powerful the bond between the individuals involved. You surely wouldn't deny that, even in purely animalistic terms, there is a distinct advantage in the societal structures we have built up on the basis of our strong and powerful bonds as human beings.
I think it's wrong to make out that human beings are somehow special and gifted in a way that other animals aren't. I agree that we have particular advantages and traits that other animals do not and that we should use those to their fullest potential, but this shouldn't convince us that we are somehow special, that the universe revolves miraculously around us. It's akin, I think, to suggesting that God owes us something.
As for death, it makes sense that we die, and it makes sense that we don't want to die. If didn't die, we'd be grossly overpopulated and would suffer for it, and if we didn't mind dying we'd just let it happen and all be dead. Where's the mystery in that?
