I just joined this topic, but will throw out my 2 cents.
The prove it stance is definitely not the only one an atheist can take. There are many more, at least for me. I just simply look at the world around me. For instance, did you know that there are berries that are very tasty that kill you? Well, there are and there are lots of them. I have to ask, what kind of parent puts a tasty cake(berry) in the middle of a kids house(world) with poison in it? Wouldn't the energy put into making tons of poisonous plants be better used to, oh I dunno, make more edible plants for the starving? Think about the millions of people who died from bad plants through the centuries and God never thought it important enough to give them a plant guide.... Poor people, bad God.
Secondly, how can God be all loving while putting poisonous plants on the Earth? His book is full of contradictions, he commanded mass genocide of people, he floods the earth and chooses insane people to spread his message(John the Baptist and Paul were not very good candidates).
Just consider your teeth for a second. God made our teeth strong and capable of chewing, he gave up grinders in the back and front teeth strong enough to move the food to the back. Then God decided to give us wisdom teeth hmmm, then he decided that plaque was necessary, then he created gingervitus.
If you still fail to see that the "show me proof" argument isn't the only one, I suggest you shadow a doctor in any hospital. He will give you about a million reasons why he doesn't think a loving God exists.