It seems to me that every time someone is cured of some disease and the onlookers say "It's a miracle and proves that God exists" - these people must be ignorant of the Douglas Adams "Babel Fish" argument.
Mike, you need to hope that we cannot ever prove that God DOES exist, because the moment we do, His son's "only through faith" disclaimer is proved to be a lie, which completely destroys any chance of His existence. And we don't know if, at the time Jesus said those words, He was speaking as the Son or the Trinity - since the three are one. But if that was the Trinity speaking, then all three are destroyed at once by finding even the smallest scintilla of proof. And that is enough to show the absurdity of it all, which is (dis-)proof enough for me.
Except I am not discussion the Christian religion. Note I have said many times...Gor or gods or whatever...
As to not be able to prove a negative can't you prove the following:
80 cms does not equal 3 ft
300 grams does not equal 1 pound etc.
In the case of an atheist he/her has insufficient evidence that anything outside physics exists and that results in a belief etc.