This often confuses me as well. Why would an atheist in America choose to target the Christian god rather than say, Thor or Zeus or Krishna? It simply makes no sense. It's not like Christianity is the dominant theistic worldview here.
There is some truth to this. Carrier argues the same ideas I've been arguing. Although it's funny that you mention confirmation bias. The whole point about outsourcing the production and assimilation of knowledge to method is that method serves to minimize bias.
Proper method is the answer to bias, where "proper" is justification through consistent long term trial and error. The entire purpose of using method is because we're biased, and that idea is core to metaphysical naturalism. Unless we minimize our bias through use of proper method, we have no trustworthy way to tell if our beliefs are true or false.
Still, there's some truth in your words. Minimizing bias does not mean eliminating it. Although I'd challenge you to compare what you believe, and we can see who has more bias.
As I said earlier in this overview thread, be specific. You haven't shown him to go against his own advice/criteria yet. You've mistakenly believed that was the case in a few posts. Resurrect those posts if I didn't explain the position thoroughly enough.