On CMI, the article "Atheism", I found this assessment:
Early Christians were referred to as “atheists” because they did not believe in the Greek or Roman gods. Yet, while they positively affirmed the non-existence of those gods they likely believed that those gods were deceptive demons whom they did believe existed (1 Corinthians 8:4–6).
Actually, the major Greek and Roman god they were required to and refused to believe in was the Emperor's Genius.
And as far as I know, they did not deny that Tiberius or Nero were men of flesh and blood.
First Epistle Of Saint Paul To The Corinthians, Chapter 8:  But as for the meats that are sacrificed to idols, we know that an idol is nothing in the world, and that there is no God but one.  For although there be that are called gods, either in heaven or on earth (for there be gods many, and lords many).  Yet to us there is but one God, the Father, of whom are all things, and we unto him; and one Lord Jesus Christ, by whom are all things, and we by him.
That was Douay Rheims, now to KJV:
4 As concerning therefore the eating of those things that are offered in sacrifice unto idols, we know that an idol is nothing in the world, and that there is none other God but one. 5 For though there be that are called gods, whether in heaven or in earth, (as there be gods many, and lords many,) 6 But to us there is but one God, the Father, of whom are all things, and we in him; and one Lord Jesus Christ, by whom are all things, and we by him.
Here is The Complete Jewish Bible:
4 So, as for eating food sacrificed to idols, we “know” that, as you say, “An idol has no real existence in the world, and there is only one God.” 5 For even if there are so-called “gods,” either in heaven or on earth — as in fact there are “gods” and “lords” galore — 6 yet for us there is one God, the Father, from whom all things come and for whom we exist; and one Lord, Yeshua the Messiah, through whom were created all things and through whom we have our being.
Now to the commentary thereon:
- Ver. 4.
- An idol is nothing. The apostle seems to allude in this place to the Greek signification of this word, eidolon, signifying a false representation; as for instance in ghosts, which are said to appear sometimes at night. Umbrœ tenues, simulacra luce carentium. (Calmet)
- Ver. 5.
- Many gods, &c. Reputed for such among the heathens. (Challoner)
- Ver. 6.
- To us there is but one God, the Father; of whom all things, and we unto him. Of or from the Father are all things, even the eternal Son and the Holy Ghost, though they are one and the same God with the Father.
And one Lord Jesus Christ: by whom are all things, and we by him. All things were created by the Son of God, the eternal and uncreated wisdom of the Father, from whom he proceeds from eternity, and also by the Holy Ghost, all creatures being equally the work of the three divine persons. The Arians and Socinians pretend from this place, that only the Father is truly and properly God. The Catholics answer, that he is called the God, of whom all, because from him always proceeded, do proceed, and shall always proceed the Son and the Holy Ghost, though one and the same God in nature, substance, &c. And that when he is called the one God, by these words are excluded the false gods of the heathens, not the Son, and the Holy Ghost, who are but one God with the Father. St. Chrysostom also here observes, (hom. xx.) that if the two other persons are excluded, because the Father is called one God, by the same way of reasoning it would follow, that because Jesus Christ is called the one Lord, neither the Holy Ghost, nor even the Father, are the one Lord, whereas the Scriptures many times express the divine majesty, as well by the word Lord as by the word God. (Witham)
Now, none of the versions and none of the Catholic commentaries actually say in so many words "Yet, while they positively affirmed the non-existence of those gods they likely believed that those gods were deceptive demons whom they did believe existed".
For some of the pagan gods this is very straightforward.
Apollo gave prophecies which drove Laios and Oedipus to attempted killing of son and real unbeknownst killing of father. Which drove the grandfather of Perseus to try to prevent his being conceived and born. Which drove Orestes first to killing of mother and thereby to what could have been either madness or real persecution by real demons (what is called "demonic obsession," as opposed to "demonic possession" when demons take control of the victim's body), after which Apollo seems to have appeared as one of the parties in a court, other party being the Furies (the demons persecuting Orestes), judge being Athena, goddess of the city and outcome being Furies getting a CULT of worship in Athens in return for accepting to have been defeated by Apollo. And Apollo also agreed to this.
- Humans :
- Orestes among others.
- Demons :
- Apollo, Furies, Athena. All of which worshipped as gods.
Note that other stories featuring Athena may signifiy other things. When Athena gives council (not magic aid, but council) to Ulysses, it could have been a demon, but could also have been a guardian angel, working through a shape from which Ulysses was ready to take advise. And when Athena was spinning along her friend Arachne, originally this was about two maidens in Athens who were very good at spinning.
- Humans :
- Ulysses, Athena (1), Arachne
- Demon OR guardian angel :
- Athena (2)
- Worshipped as same goddess :
- Athena (1+2+3, see above the Orestes case).
And what happens when a Pagan is sacrificing to Apollo or Athena and then gives away the meat to the poor?
At worst, a demon is there, but at best, nothing at all. This is the case St Paul was talking about. The verses do not give a general theory about all there is in Paganism, and do not even mention the case of mythological stories or how we stand to these. They are about the general concept of other things than God being called gods and about the practical consequence thereof, idol worship. They do not specify what exactly these things are instead, unless you take "whether in heaven or in earth" as referring to Christian explanations (some divine interventions, some demonic ones) rather than the Pagan division between celestial and chthonic divinities.
Why is this important?
Because the New Atheism, among others basing itself on the charge of "atheism" against Christians, has declared "Christians are atheists about all gods except one, we just take it one step further". That may be very true for Enlightenment and Post-Enlightenment Christians who think that for instance not just it is wrong to worship at the altar of Helios, not just is Helios not a god, but he is not even a person taking the visible solar object on a ride. But this was not the attitude of the first Christians. Nor were they saying that "Tiberius" was a pure myth, or that "Nero" was such. And similarily, they were not denying that Hercules and Romulus existed. Though especially of the former, or of his ancestor Perseus, when it is said he and Andromeda were taken up to the stars, they did say that the devil added lies about them.
This is not a matter of pure speculation on my part, it is a matter of looking up the Church Fathers. References will be added later, in comments.
This truth is of course highly unwelcome to two kinds of people : Atheists who claim to be "atheists about just one more god" than we, and Christians who want Christians to be fideists.
By the way, another kind of Anti-Christian argument also would not find it welcome if my position here were widely known. Those who (like Richard Carrier) argue that supernatural legends are likely to come about without any reference to fact. Those who argue "if Greeks could invent Hercules out of nothing and connect him to later Spartan Kings, if Romans could invent Romulus and Remus from the mere name of their city and consider the first as the first of seven kings, why should not Christians have invented Jesus out of nothing?"
And my answer is Greeks and Romans were - as far as historical narrative is concerned, as opposed to theology - just marginally wrong about very real and very historic persons called for real Herakles (or however that was pronounced 500 years before Homer) and Romulus (presumably Romlos or Romelos?). Only in theology, in worshipping Hercules and Romulus, were the Greeks and Romans versy wrong, but in history there were just marginal traits which would need weeding out before Hercules and Romulus are reduced to human types of "very strong man" and "very surprising avenger". Nothing like what an Atheist would need to weed out of the Gospels.
Hans Georg Lundahl
St Peter of Alcantara