Hilarius, your friend is correct to some degree. If we are absolutely certain that God doesn't exist: then if there is only one alternative explanation -no matter how unlikely- it must be true.

Of course it isn't important to prove it if you follow this mentality - You've already proved it by means of elimination.

For such a person the bible solution was never an option in the first place.

Yes, many Atheists behave like that, but definately not all. And this behaviour pattern is not limited to Atheists by any means. This behaviour is exactly the same as what Atheists often accuse Christian Fundamentalists of doing.

You've misunderstood the nature and need of proof. First, the one asserting must do the proving. If you assert that there is a pink unicorn in your bathroom, it is not incumbent on me to prove you are wrong. You must provide positive evidence for the existence of the unicorn. For most assertions such proof is not necessary, because they do not entail violations of common sense or natural law.

Similarly, Christians assert that Jesus was crucified for my sins. That entails proving that there was a Jesus, that he was crucified, that I have sins, and there is some cosmic framework where his death could do that. Try proving nonsense like that!

Atheists don't have to do anything. Your friend is right. We don't have to prove that Jesus never lived, or that we have no sins.
Mere construction of alternatives is enough to act as strong evidence that the Xtians have no case.

Take Sai Baba, the Indian holy man. Any magician can tell you that not one of his tricks is difficult for a trained magician.
I don't have to prove that Sai Baba is actually using mundane methods to do all his tricks (though that has actually been done in some cases). I only have to show the strong possibility. It helps my case, on a practical level, to actually have evidence in a couple of instances, and we do have tapes of him cheating. So we can safely put the rest of his tricks in the "clever magician" box too.

Rather, Sai Baba's disciples are left in the awkward position of demonstrating that although mundane methods can replicate all his tricks, he is nevertheless using special powers to do them. Xtians are in the same position with regard to Jesus, as well as having the additional problem of demonstrating "sin" and some cosmological framework where atonement of my sin through the death of an itinerant preacher actually makes sense. Good luck!

Michael