You're fighting a losing battle. This guy is a raging fanatic who oppresses all viewpoints other than his own. No rational persone questions whether Jesus lived or not. Rather, such talk is just an attempt to diminish the spiritual beliefs of others. His motive is simple and obvious. The dude you are fighting is so devoid of any spiritual life and empty inside that he feels the need to attack others to better convince himself of his own righteousness.

Toxicity label: other