Do dragons exist? Unicorns? Faeries?
How about good, evil, heaven, hell, gods, demons, angels, or devils?
How about the monitor, the keyboard, or the mouse?
My beliefs affect you. Your beliefs affect me. It may be convenient if our beliefs agree, but that's not a prerequisite.
An intersection with a four-way stop. She pulls into the intersection believing that he will stop. He does not. Crash!
A crowded sidewalk. She believes that if she steps on a crack, she will break her mother's back. He wonders why that lady is walking funny and holding up the flow. He is in a hurry and needs to get by. Bump...
He is afraid to ask, afraid of how she might respond.
Your acceptance, denial, or indifference toward religion won't stop the Jehovah's Witnesses or Mormons from knocking on your door...
In some sense, it does not matter what I believe. If you believe in something, then that something does exist---for both of us.