Let's go line by line: "The wrath of God is being revealed from heaven against all the godlessness and wickedness of men who suppress the truth by their wickedness," Calvinistic: Everyone suppresses the truth from birth (Total Depravity), so this is just God revealing his wrath against all fallen humanity. Non-Calvinistic: God is revealing his wrath against people who actually suppress the truth. "since what may be known about God is plain to them, because God has made it plain to them. For since the creation of the world God's invisible qualities--his eternal power and divine nature--have been clearly seen, being understood from what has been made, so that men are without excuse." Calvinistic: All men are dead, blind, and deaf to the things of God from birth and thus cannot clearly see or understand God's revelation of himself, but they are still held accountable ("without excuse') because Adam represented them in the Fall. Non-Calvinistic: God's revelation is clearly seen and understood, so all men are without excuse. "For although they knew God, they neither glorified him as God nor gave thanks to him," Calvinistic: The natural man cannot know God. Non-Calvinistic: The natural man can know God and understand his revelation, but choose to refuse to acknowledge him as God despite that clear revelation "but their thinking became futile and their foolish hearts were darkened." Calvinistic: Their thinking has been futile from the womb and their foolish hearts were darkened from birth due to the Fall. Non-Calvinistic: After rejecting the clearly revealed truth and rebelling against the revelation they obviously understood, their thinking became futile and their foolish hearts were darkened. Based on this alone, I think it can be correctly argued that Paul was not a Calvinist.