Why aren't there existing letters of Atheism like the ones written by St. Paul?

You haven't been studying your ancient history, have you?

Anaxagoras

Xenophanes

Prodicus of Ceos

Protagoras

Diagoras of Melos

Theodorus of Cyrene

Euhemerus

Leucippus

Democritus

Euripides

Aristophanes

And those are just some of the Greeks.

Unbelievers at that time didn't tend to live long, and anything they wrote would have been destroyed by the religious establishment.

There were centers of pagan learning, equivalent to today's universities, that were destroyed by Christian mobs. Don't claim to have invented something when all the Christians did was take over an institution they destroyed and use it for their own purposes.

atheism isn't a religion. we don't have a religious book. we have books written by people like Dawkins, Hitchens, DeGrasse Tyson, and Nye but not a book of made of holiness and magic tricks and stories of spirits knocking up virgins.

Back in the day they killed unbelievers so I'm guessing they weren't really bin into letter writing. In any case, why does that matter?

Because atheism isn't a religion.

There are, but you're too lazy to look. Laertius wrote of the philosopher Epicurus and his teachings three hundred years before Christianity.

Is God willing to prevent evil, but not able?

Then he is not omnipotent.

Is he able, but not willing?

Then he is malevolent.

Is he both able and willing?

Then whence cometh evil?

Is he neither able nor willing?

Then why call him God?

Mankind of one sort or another is over 2 MILLION years old, modern man 200,000 years old, Christianity just 2,000 years old with Islam an even younger 1,400 years old!

If it was not for man god would not have been invented!

Sift through the ashes at the bottom of the stake.

There are many, if you bother to look for them.

Unbelievers were killed, and their writings destroyed.