They deny it, A Dot, because they have not the courage to examine their beliefs honestly.
Do they honestly understand that the concept of Hell, unknown in the Old Testament, was the result of the Greco/Roman concept of Hades, incorporated into Christianity? They do not.
Do they understand that the history of Jesus was in no way original, unique, nor likely true?
Do they understand that the god they follow is self-contradictory? Evil as hell in the OT, and somewhat more mellow in the NT, except for the abominable and heartless concept of Hell?
A, the argument is over among intelligent people. The Jesus myth has been relegated to the thick books of all the other mythologies that have plagued humans for tens of thousands of years. We made them all up, we can put them away. And so we shall. And so we have. We reasonable, rational people will go on in the light of discovery, subject to enlightening change. Any other way is stifling and appeals to the worst instincts and values of the human beast.
It will take time, but someone has to blaze this trail. I nominate you.
The single thing that is responsible for creating more atheists than any other cause: The Holy Bible. Any thinking person who reads this truly awful and detestable book cannot possible emerge from the experience as a religious person.