First I'll say that paganism does have some correct ideas about God, but mixed in with idolatry - the worship of statues that represent false gods. Idolatry generally includes immoral acts as part of worship. Here is what Paul said.:
Paul Addresses the Areopagus
22 So Paul, standing in the midst of the Areopagus, said: “Men of Athens, I perceive that in every way you are very religious.23 For as I passed along and observed the objects of your worship, I found also an altar with this inscription, ‘To the unknown god.’ What therefore you worship as unknown, this I proclaim to you. 24 The God who made the world and everything in it, being Lord of heaven and earth, does not live in temples made by man,[c] 25 nor is he served by human hands, as though he needed anything, since he himself gives to all mankind life and breath and everything. 26 And he made from one man every nation of mankind to live on all the face of the earth, having determined allotted periods and the boundaries of their dwelling place, 27 that they should seek God, and perhaps feel their way toward him and find him. Yet he is actually not far from each one of us, 28 for
“‘In him we live and move and have our being’;
as even some of your own poets have said,
“‘For we are indeed his offspring.’
29 Being then God's offspring, we ought not to think that the divine being is like gold or silver or stone, an image formed by the art and imagination of man. 30 The times of ignorance God overlooked, but now he commands all people everywhere to repent, 31 because he has fixed a day on which he will judge the world in righteousness by a man whom he has appointed; and of this he has given assurance to all by raising him from the dead.”
32 Now when they heard of the resurrection of the dead, some mocked. But others said, “We will hear you again about this.”33 So Paul went out from their midst. 34 But some men joined him and believed, among whom also were Dionysius the Areopagite and a woman named Damaris and others with them.
So, Paul took a couple of phrases that should have been familiar to them. He then showed how it should have been obvious to them that idolatry was wrong. They were being inconsistent in their worship.
Some were willing to listen to more, but others mocked the idea of the resurrection.