I think the basis of the problem is, atheism is rational where religion is not. Therefore, it doesn't make a lot of sense for atheist to feel the need to defend their postition(s).
                Religion, on the other hand, is totally irrational, so it makes a lot of sense for them to feel the need to defend it. The other issue is, because it's irrational, they are always afraid of losing their faith, so their constantly trying to duct-tape the blinders. Reality is a really bad thing to them.