Romans 1:18-32 KJV

¹⁸ For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who hold the truth in unrighteousness; ¹⁹ Because that which may be known of God is manifest in them; for God hath shewed it unto them. ²⁰ For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse: ²¹ Because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened. ²² Professing themselves to be wise, they became fools, ²³ And changed the glory of the uncorruptible God into an image made like to corruptible man, and to birds, and fourfooted beasts, and creeping things.

²⁴ Wherefore God also gave them up to uncleanness through the lusts of their own hearts, to dishonour their own bodies between themselves: ²⁵ Who changed the truth of God into a lie, and worshipped and served the creature more than the Creator, who is blessed for ever. Amen.

²⁶ For this cause God gave them up unto vile affections: for even their women did change the natural use into that which is against nature: ²⁷ And likewise also the men, leaving the natural use of the woman, burned in their lust one toward another; men with men working that which is unseemly, and receiving in themselves that recompence of their error which was meet.

²⁸ And even as they did not like to retain God in their knowledge, God gave them over to a reprobate mind, to do those things which are not convenient; ²⁹ Being filled with all unrighteousness, fornication, wickedness, covetousness, maliciousness; full of envy, murder, debate, deceit, malignity; whisperers, ³⁰ Backbiters, haters of God, despiteful, proud, boasters, inventors of evil things, disobedient to parents, ³¹ Without understanding, covenantbreakers, without natural affection, implacable, unmerciful: ³² Who knowing the judgment of God, that they which commit such things are worthy of death, not only do the same, but have pleasure in them that do them.

At the risk of posing a question that may have been asked previously, but with perhaps a different slant, and fleshing it out a bit, who, exactly, is Paul referencing here? Notice that whoever these people are, Paul refers to them as "they", "them" and "themselves" as if his audience already knows who they are. Also, notice that much of this discourse is in the past tense; "when they knew God", "they glorified Him not as God", "neither were they thankful", "but became", "they became fools", "changed the glory", "God gave them up", "who changed the truth".

This sounds at first like a specific demographic who is behaving in a specific manner at a time in the past more so than the present or future. This really can't be referring to Jews because Jews generally believe in one God who is the Creator, regardless of how "righteous" they are or aren't. Is this aimed at atheistic, sinful Gentiles? Do atheistic, sinful Gentiles "really know there is a God", deep down in their hearts? Really?

I have read some commentaries that suggest that those being referenced by Paul here were the vast majority of people who lived prior to Noah's flood, whom God drowned in the flood precisely because those people back then did know God and refused to acknowledge Him. God walked with mankind in general before the flood and made Himself known. He did not "hide Himself" prior to the flood. So those people truly had no excuse. But after the flood, God withdrew Himself from man except for select individuals called to be prophets and a few righteous kings.

So I don't see how Paul can be referring to any or all disbelieving, sinful Gentiles past, present, or future here. And even if he were, what interest would Paul's Jewish audience have in disbelieving, sinful Gentiles? The pre-flood argument is the only one that makes sense to me. Feel free to edit this question as you all see best.