I used to think this way. "I won't read Mein Kampf because I might turn out a Nazi." This is actually a very insidiously bad mindset. You should believe any argument that can convince you (in fair conditions -- reading Mein Kampf in a calm frame of mind in your own living room, as opposed to under conditions of intimidation in Nazi Germany.) If Nazism is awful, it will still be awful even when you know more about it. And, indeed, most of us don't turn into neo-Nazis when we read Mein Kampf.

Sure, we have bounded rationality. But I don't see how, in probabilistic terms, you can be more likely to get it right without accumulating more evidence. (Maybe your priors are wrong.) If you really think you couldn't stand up to debate with a talented missionary, maybe you aren't really an atheist; maybe you should be glad to change your mind.

Psychologically, I think it's much better for people to trust their reason in this way. It makes it possible to live with more courage. I don't want to live with my head down hoping I won't be exposed to the wrong things.