John, you did lose that round. And the reason is that you fell into the trap of numbers of believers or lack thereof somehow being proof of the rightness or wrongness of beliefs.
At one point, everyone on Earth likely believed the planet was flat. They were all wrong.
It was a good response on his part.
A parry and thrust might have been, "You know, all of the heroes of the Bible--from the prophets up until Jesus--were noted for courageously speaking out about the religious hypocrisy of a nation dedicated to God but that had fallen away from true, pure worship. Where are these heroes today?"
If he tried to say, "We speak out against Christendom ..." the BIBLICAL response would be, "No, you don't get it. The heroes of the Bible didn't speak out against false beliefs and practices of OTHER nations. They spoke out against the religious hypocrisy and cowardice of their own leaders!"
Just remember, they killed Jesus for his outspokenness. Your mileage may vary.
Let's review: It's a cult!