"The Atheist waits for proof of God. Till that proof comes he remains, as his name implies, without God. His mind is open to every new truth, after it has passed the warder reason at the gate."
- Annie Besant
Quote Source: "The Atheistic Platform", Twelve Lectures
It's not that I don't appreciate the sentiment of this quote, but I think that, like others have pointed out in the forum, implying that Atheists are inherently open to more possibilities than theists is kind of a logical jump to make. I may be confusing my definitions a little bit, but isn't an Atheist one who firmly believes there is no God? that doesn't so much imply the openness to alternative ideas, just a conviction against a single one.
I think you are on to something there Sammy, atheist do not believe in deities. Agnostic people don't know and more or less await proof one way or the other. Making a decision either way enough to say there is no god or there is one take a certain amount of closed-mindedness. I will argue that religious people and atheist can be open-minded as well but tend to be closed minded when it comes to certain subject matter mainly pertaining to the existence of God.
On the contrary, my mind is generally closed to all of the so-called new truths that come my way. This is mainly because after hearing it all so many times being shoved down our throats, we tend to discount every new idea that comes along.
I think it is healthier to keep an open mind and try to do so, I also find a degree of skepticism to be a good thing too.