If you're a Christian, have you read the Koran/Qu'ran? If you're Muslim, have you read the Bible?

Have you read Jainism's Jain Agamas, Hinduism's Bhagavad Gita, Mayan's Popol Vuh, Sikhism's Guru Granth Sahib, Tenrikyo's Ofudesaki, or the Book of Mormon?

Humanity's writings on mythology is prolific, and yet you've decided that one of them is true. Have you read all of the holy books for all religions humanity has ever written? Why do you dismiss them all while accepting yours?

Many atheists have read the Bible. Many would cite doing so as an important step towards their atheism. Many study it just to understand where their fellow citizens are coming from, and like to understand the cultural heritage of humanity.

Beyond that, it's a question of practicality. As people, we often have better, and more important things to do with our time, energy and money than familiarize, intensely study, and painstakingly assess evidence for/against thousands of mythologies.

Assuming an atheist hasn't read the Bible or Qu'ran, the next step is to have it survive the "elevator pitch". Life is full of absurd claims - from homeopathy, dowsing, and crystal healing... to ghosts. Before any reasonable, rational person is going to invest any time in your claim, you must be able to demonstrate, on a minimal level, that there's anything to your claim - some type of evidence - that isn't rife with easily-identifiable logical fallacies.

In many ways, it's analogous to applying for a job. Job applications go through a series of stages, from an initial cover letter and resume, to phone interviews, to in-person interviews. If the initial resume or cover letter is junk, that person's application will probably be immediately discarded. Why waste company time/resources into hiring that person, just to see whether he/she can do the job, when the resume doesn't indicate any competence from the outset? This point is especially important, when the company has hundreds to thousands of applications to sift through.

We face similar pragmatic issues when dealing with the plethora of claims we face on a daily basis. Your claim's "cover letter" must have something to it, that indicates there's anything of value to investigate - to dig deeper.

Until that happens, we're valid to dismiss your claims alongside the other then thousand ridiculous claims that surround us from day-to-day.