Romans 1:18-32 and Wisdom of Solomon
The incredibly strong similarities between Romans 1:18-32 and Wisdom of Solomon 13-14 have long been noted by scholars. Paul appears to be deliberately quoting (paraphrasing) a Jewish piece of anti-gentile propaganda.
Isn't that a strange thing for Paul to do? Yes. We would expect Paul, the apostle to the Gentiles, not to agree with such anti-Gentile and pro-Jewish sentiments.
Indeed, immediately after the quote, Paul launches into a critique of people who hold the quoted view.
Romans 1:18-32 seems to be an instance of an ancient literary device called "speech-in-character" (prosopopoeia). Or, more simply put, is what we would call a "dialog" or "debate", with Paul deliberately presenting an opposition viewpoint and responding. It is now well-established that in Romans 7 Paul uses a lengthy speech-in-character without warning his readers. Equally, in many part of Romans that take a question and answer format, Paul is obviously engaging in a pseudo-dialog with opposing viewpoints.
Seeing Wisdom of Solomon as representing Paul's ongoing debate opponent through the rest of Romans 2-4 is particularly helpful. Wisdom 15-19 takes the view that God has chosen the Jews, protects them from sin, and that as a result Jews do not sin like the Gentiles do. It is exactly such a viewpoint that Paul is arguing against in Romans 2-4 - he asserts that there is equality before God and that the Jews do not enjoy special sinlessness.
A important point is that Paul has no need to prove that every human individual sins (hence the oft-observed fact that his argument fails to prove this is irrelevant). Rather, he wants to prove that some Jews in history have been particularly sinful on occasion and that therefore the Jews as a people are not protected from sin simply by virtue of being Jews as Wisdom of Solomon claims.
The long and the short of this is that Romans 1:18-32 is not Paul speaking (just like much of Romans 7), and that Paul in fact disagrees with the speaker on many issues, and the speaker becomes Paul's debate partner for that section of Romans.