Whoo! So many answers, I would never have thought that this could be such an agitated discussion
I would like to give my two cents as well.
About sex, I think we can sum this up in the more general word: Fun! Spend life having fun, joy, pleasure, delight, whatever. Simply to enjoy life. That is a purpose, alright, as long as you have the ability to enjoy life. But what if you cannot? Possibly because you have to work 7 days a week, 16 hours a day? Or because you live in the fourth world, not being able to imagine how you will survive tomorrow? How can there be any joy whatsoever?
About the afterlife: I was not exactly hinting toward any religious assumption about an afterlife. On the contrary, I think that this is not at all a topic directly related to religion. Science has sought to find answers to the eternal question: Is there an afterlife, and if so, what is it like?, but so far, everything does not quite seem appropriate. And for all the claims that religions make (I am a catholic, btw.) about an afterlife, I do not think I will ever be able to believe any of them, until I actually have died. But until then (whenever that may be) I will just have to put with the uncertainty, and possibly the fear, about 'what's next'. But as hard as I try: I simply cannot believe that it will just be 'over'. There has to be something. I find it hard to believe, that my consciousness, my perceiving, experiencing ego is simply the end-product of the complex operations of all the cells, chemical transmissions and neural processes that go on in my brain. If that were so, it should in theory be possible to create just that consciousness with a computer - an artificial intelligence.
Well, now. Enough babbling, but I would be curious to know your thoughts.