people often become atheists after having studied religion without a confirmation bias.
Unless either one of us can provide non-anecdotal evidence for this being the case or not, this point probably isn't going to go anywhere. All I can say is that, after having belonged to several atheist communities over the years, this has not been my experience.
that, was why I became an atheist.
We're describing the same experience; I'm just using more derisive terms.
Forgive my presumptuousness, but I'm guessing you learned more about history or anthropology than theology--the former of which has no bearing whatsoever on the truth of any of religion's propositions. Feel free to correct me if I'm wrong.
"the best way to become an atheist is to read the bible"
Penn Jillette was, as well as he did a slew of other asinine comments.
It's called new(/vulgar/discount-store/an idiot's caricature of) atheism, and it's motivated more by politics and pent-up resentment against religious parents than theology. People who care enough about religion to become intimately acquainted with it generally aren't Atheists--or, at least, not the kind of Atheists who waste their time arguing bush-league philosophy with believers.