Notice this question never gets directly answered. How much do you need to know about fairyology before you are allowed to disbelieve in fairies? The truth according to religious pundits like Eagleton is "I can't answer that question without compromising my position, therefore I will continue to misdirect with vague allusions about what hypothetical atheists may say". Fortunately, you have Brad here to illustrate that. People on both sides of the issue understand what that question really does, which is redefine the terms of the debate in terms that are totally unacceptable to Christians. That's why Dawkins does it, and that's why Eagleton dodges it.