Mankind has been inclined to say "There is no god" for a long time,
in fact the concept predates Christianity.
We think there is no God because that is what we have been taught to think. Many Scientists are devoting themselves to trying to prove life as we know it could have developed from chemical reactions.
Even so, creator-less evolution is still being taught as fact, with no mention of the difficulties. By the way, I don't blame Darwin; science at the time had only begun to fathom the intricacies we now know of in a single cell, much less what we will learn in the future. Besides, he only claimed it as a theory, and hoped in time, scientists would discover the "missing links" that should exist if it is true.
We think there is no God because we cannot see Him, cannot touch Him, and cannot measure Him. Did radio waves exist before mankind learned to detect them? Can we see, touch or measure love?
So, how can we know He's real? Well, have you ever tried asking Him? No, don't ask Him to spell out your name in clouds. That would only confuse those with the same name who didn't ask. Think of something quiet and private, just between you and Him.
Keep in mind He's not a genii or some sort of cosmic vending machine, obligated to do whatever you ask if only you use the right magic words. But if you're sincerely seeking Him, He will make himself known to you.
We hope there is no God, because then there's no one to whom we are ultimately accountable. If there is no God, we think, then perhaps there is no such thing as "good" and "evil." Lack of accountability opens the door to doing whatever one thinks one can get away with. Sounds like fun, but only if most of the rest of the population keeps on doing the "right thing" without the authorities looking over their shoulder. Otherwise, the whole system begins to fall apart. Ask the Russians.
We doubt there is a God because
things happen that are inconsistent with
our concept of what a god should do.
Let's not forget that an eternal God who can create a universe,
who knows the end from the beginning,
who designed us and created us,
has got to have a better view of things
that we mortals of limited intellect and experience, who are stuck in three dimensions and
subject to the passing of time.