Grumble Grumble Grumble
The heart of the problem is the following truth... "Religious belief is based on faith, not logic"
Now philosophers and learned men of religion have been trying to logically prove the existence or nonexistence of God for centuries, from the introduction of Greek logic. And so far, the only thing that has been proven through logic is the agnostic position (It is not logically possible to either prove or disprove the existence of God)
Atheism and Christianity are diametrically opposed beliefs. If one is correct, then the other must be incorrect. And of course people who have strong feelings for their belief would want to prove that the challenge to their belief is incorrect... But with either position being based on faith, (though many Atheist have the mistaken belief that if you can't logically prove the existence of God, that proves the nonexistence of God. This concept is logically flawed), it's not logically possible to prove or disprove either position.
And yes, it is hard to have a discussion on religion with an agnostic, because all they do is point out logical flaws in your argument without taking a positions on their own. (But that what agnostics believe in!!!) Very much like talking to Quality Assurance Engineers... (How many Q.A. Engineers does it take to change a light bulb? Answer: None, they only report the problems, they don't do anything to fix them...)
As for seeing a ghost?? How would I know if I saw one? What are the characteristics of a ghost? How can I measure one? The philosophy of using the rules of logic to view the world (otherwise known as SCIENCE) requires phenomenom be defined in a consistent and observable fashion. Until someone comes up with a universally agreed definition to measure and observe 'God', Science cannot provide any information on it's existence...(or nonexistence...)