... I might respond as follows:

I can say with certainty there's no Zeus, there's no
Allah, there are no ghosts or goblins or (the list is
quite long) ... because all of the evidence points to
creation of said concepts by humans, for humans,
in this life, on this earth, in all times past and present
that human imaginations have been played out in the
form of words and symbols. Even today, people
spin ET fantasies and claim for all they're worth
that they've been abducted into alien spaceships.

The logical and reasonable explanation for all of the
fantasy constructs of humankind reside in a natural
world and the human mind.

Look closely there, think about how easy it is to use
the "truth meme", and determine for yourself, outside
the propaganda of the church/god meme machine, is
_____________ (insert claim here) true?

Once you accede to the blind faith journey, you're
destined to forever be off in the "I must allow for it to
exist" world and claim your lack of disbelief regarding
*all* fantasy constructs unless

1) you accede to a demand for you to deny all fantasy
constructs other than the one you've bought into (this
especially relates to the christian/jewish/[and probably
islamic-not sure about that one] demand to put no
other gods before me (me being YAHWEH or some
such super-being that humans came up with to wow
[overwhelm] the natives as it were) -or-

2) unless you're picky about your fantasy constructs
and pick and choose based on a variety of social /
financial / sexual / cultural reasons with none of them
having any piece of *real* and tangible experiential
non-partisan evidence (such is the case with imaginary
beings as *real* and tangible experiential non-partisan
evidence does not exist for said beings' existence)

Here's an imaginary being for you, if you're into the
mood of asking "How Can You Say There Is No
_____ (fill in favorite imaginary being here)?"

Fud.

How can you not believe in Fud? You see, Fud being
the ultimate being, it created God and like a spoiled
child, God went off and spun up a universe he could
neither control or interact with in any meaningful way...

And on and on and on with the fantasies and creations
of the human imagination ... In the modern age, folks
don't, for the most part, claim to be hearing from
deities guiding them to write holy scripts and dictate
to humans. In days gone by, humankind was ripe for
the picking with superstition and fear ruling the day.
Such is the day when gods / God / etc. were created.
I can see that as clear as my image in a mirror. I know
that the image in the mirror is a reflection of reality.
There is not another "me" in that mirror.

You would not scoff at my claim that my reflection
is explainable based on physics in a real world. Why
would you be eager to scoff at my claim that *all*
imaginary beings, including the most powerful and
super of them - the deity gang - are reflections of
the human imagination in a real world?

The answer to that question resides in the nature of
the fantasy constructs you've subjected yourself to,
for in there all of the traps have been laid to suck you
into belief *at all costs*, for inherent in consideration
of disbelief and doubt is that fantasy blackmail/threat
of oblivion/hell that you've been guilt-tripped into
believing is yours to risk if you dare to flirt with
disbelief ...

... WARNING PROCEED WITH CAUTION ...
Once you buy into the god/christ fantasy, you're
basically trapped/imprisoned/enslaved in your blind
faith for such is the design of the faith. It's quicksand
to rob you of your control over your life and the
only way for you to get out of that trap is to grab
hold of the branch of logic and reason that I'm
offering and pull yourself out - I'll help if I can but
you cannot get out unless you're willing (brave
enough) to grab hold of logic and reason and
sanity and reality for all you're worth.

Think different. You can escape - I and many others
have. The decision is yours. Choose wisely.