The second sentence of this response is a non-defense of your thesis, and the rest of it does not help your case, much. I am open to evidence of your claim that "many" have become atheists. For the sake of argument, I would admit that >10% conversion rate would count as "many", as would, say, some absolute number such as 1,000 in the last 100 years.

Perhaps you can find some authority who has researched this question?