Comparing atheism and theism in an analogy

Imagine you wake up in an enormous cavern that is deep underground that seems to extend on forever in every direction with a river that runs through the center of the cavern which comes from a hole in the rock and exits through a hole in the rock. There is also a large pool.
Glowing edible fungus provides subsistence and light sufficient to see in dim shades of gray.

You have no memory of any other condition besides than the one that you are now in.

As you wander around you meet many people who have different perspectives about life here.

You also discover that almost everywhere there are books that talk about a place some call: "The great expanse". They talk the great expanse being full of strange plants, bright light and things appearing in alternate shades besides gray (which didn't really even make sense, since you have no concept of color). Some of it sounds very odd and incomprehensible.

A large group of people are actively digging upward to try to get to the great expanse. Different groups are digging in different directions and different tunnels.
Those who arent digging are laughing at them for digging their life away and tell them that they are wasting their time "just enjoy life in the cave" they say.

You arent sure whether you should help those trying to dig or should not dig. The people who do not dig are content to make the large cave as nice as possible and to enjoy their life their without spending a part of their day, every day, digging. You see the virtue in those who dont dig and choose to enjoy their life in the cave, but you want to know if there is anything to all of these books about the great expanse.

Some say people can actually see the great expanse if you submerge yourself in the river and float it through the hole in the rock wall and find where it leads you. Lots of people have attempted this feat. Some say that when they did this, they caught a glimpse underwater of some strange light in a tunnel that they couldn't get to-- and this must have come from the great expanse.
Others say they were washed into a tunnel which lead to a cave that was full of strange plants and light and these "alternate shades" (color). The people who had seen the light say: "You have to want truth more than you want air. You have to hold your breath underwater for as long as possible without coming out-- its the only way to be caught in the currents that lead anywhere close to the great expanse. 

Many people say that floating the river is just a waste of time because you get shot through all kinds of twisty diverging watery tunnels that all ultimately lead to the big pool. These people say that the result of holding your breath for a long time is that you will start to hallucinate a light and that people who think that they have visited a cave merely had a dream while they were passed out under water.

So you decide to do it for yourself and find out. You enter the river and you hold your breath under the water. You hold it until you are near to passing out. You want to come up for air, but you don't-- just when you are about to drown, suddenly you feel a warm current of water. Swimming towards it with all the energy you can muster, suddenly you are caught up in its current. Near to drowning, you burst open into a room full of blinding light with strange and beautiful plants. The current is still washing you in its current. 

You are not able to swim close enough to the area to enable you to touch anything, and being caught in the current you are washed back into the darkness and eventually you wind up in the same pool as everyone else arrives in back in the dark cavern.

"I saw it! Its real!" You tell people-- but many dont believe you. They respond: "you had a delusional experience", "You were dreaming", "You are lying", "You mind wanted it to be true so much that it fabricated the experience."

They ask for proof, so you try to describe the color green-- but fail miserably in describing something indescribable. Laughing, they disregard your "proof". You try to get other people to do what you did, but few do, most consider it a waste of time. They say: "Why would I do that, when I could just enjoy life in this cave?" You tell them it is an experience worth having, but they don't seem to care.

Some people try and do get a glimpse of light, others have experiences where they had time to climb the roots and exit the cave altogether, visiting with the people that live in the great expanse and return because they choose to come back down to tell people to keep digging to free the others there from darkness.

Whey you talk to people and read accounts-- now everything that they are talking about makes perfect sense-- before when you read about colors, it sounded like psychobabble, but now its like reliving your personal experiences. You read many different accounts, and find that their descriptions match your own experience.

People tell you: "Your personal experiences are not a legitimate scientific discovery". When you explain that they match the experiences of many others-- they say that all of these other accounts are also nonsense. There is literally nothing that you can do to prove your experience to anyone. People think that you are insane.