I'm an unshakeable atheist. For me, it comes down to this:
I believe that man created "God" to cope with life's challenges, that
it's extraordinarily unlikely that a God rather than a yet unexplained
scientific process created the world and is an entity who, per the
Bible, sees all, knows all, and is loving. After all, can we really
rationalize billions of painful deaths to cancer, natural disasters, etc
as "mystery beyond human comprehension," 'God's punishing man for his sins," or "God gave us free will?" I can't.
When religious people tell me about their faith, I'm faced with a decision: Do I try
to disabuse them? In my PsychologyToday.com article today, I present the thought process I've gone through.