Sin in Paul's Judaism

At first glance Romans 3:9b appears to conclude Paul's argument in 1:18-3:8: "For we have already accused all, both Jews and Greeks, as being under sin." The problem is that Romans 1:18-3:8 doesn't work well as a demonstration of universal human sin:

• Romans 1:18-32 describes the wrath of God at work in people generally, but the specific illustrations about idolatry and immorality make it clear that Paul has non-Christ-believing Gentiles primarily in view.
• In Romans 2:1-16, Paul addresses an (imaginary) individual who judges the people described in 1:18-32 but does the same things. As I mentioned earlier, I think it is significant that Paul doesn't specify the ethnicity of this hypocritical judge.
• In Romans 2:17-29 Paul addresses an (imaginary) Jew who boasts in the law but does not keep it. Indeed, his sins are flagrant violations of the ten commandments: he steals, he commits adultery, he robs temples and so causes God's name to be blasphemed. I don't see how this can be taken as a blanket condemnation of Paul's Jewish contemporaries, and I am mystified by Simon Gathercole's claim that "this Jew is not merely an individual but a representative of the nation" (Where then is Boasting?, 199).

I do not see a knock-down argument, proving beyond a shadow of a doubt that all have sinned; I see 3 illustrations of human sinfulness. They all share similar traits related to the misuse of the knowledge of God (see Keck, Romans, 88): the Gentile idolater who refuses to acknowledge God (to which Paul’s audience goes ‘uh-huh’), the one who judges the sins of others, but does not practice what he preaches (to which Paul’s audience goes, 'yeah, I guess you’re right'), and the Jewish law-breaker by presuming on God’s covenant faithfulness:

“2:17-29 is not Paul’s indictment of Judaism as such. Rather, he uses this indictment of the hypocrisy of a particular type of Jew to express the idea that simply being a Jew does not automatically confer privileged status in God’s impartial judgment” (Keck, Romans, 83).

Paul’s main concern in chapter 2 is not with showing that everyone is a sinner but with proving that God’s judgement is impartial, everyone will be judged on the basis of what they do. In fact, Paul doesn’t explicitly generalize in Romans 2 from the sin of a couple examples to the sin of everyone. The case studies lead from what is known—Gentile idolaters are guilty before God—to a conclusion (perhaps) surprising for some Jews: the covenant does not save the disobedient from God’s wrath. Again, the point is not to prove by conclusive argument that all are sinners but to demonstrate by example that God’s wrath justly falls on those who do what they know they ought not to do.

What then do we make of Romans 3:9? And how does Paul think he has demonstrated, by the time he gets to 3:19-20, that "the whole world is accountable to God"?

• (1) According to E. P. Sanders we should just give up and move on: “Paul’s case for universal sinfulness, as it is stated in Rom. 1:18-2:29, is not convincing: it is internally inconsistent and it rests on gross exaggeration” (Sanders, Paul, the Law, and the Jewish People, 125).
• (2) Francis Watson argues that 3:9 refers back to the quotation from Scripture in 3:4, which in turn anticipates the florilegium of Scriptural citations in 3:10-18:
  
  

  “The crucial exegetical point is that the references that follow to ‘the faithfulness of God,’ ‘the truth of God,’ and ‘the righteousness of God’ all derive from the initial reference to ‘the words of God.’ In Scripture God speaks, and what God speaks is an indictment of the entire human race. What is at issue is whether what God says is true, whether God is in the right in his scriptural indictment of the whole world. The scriptural indicment itself follows in vv. 9-20…" - Watson, Paul, Judaism and the Gentiles (2d; Grand Rapids: Eerdmans, 2007, 219).
  

  
  
• (3) Moo notes “that Paul characterizes his argument not as a proof of guilt but as an accusation of guilt….Criticisms of 1:18-2:29, then, to the effect that Paul has not logically demonstrated the guilt of all people are wide of the mark” (Romans 201 n. 18).
  
• (4) Stephen Westerholm thinks Paul's indictment harks back to Paul's description of humanity (not just Gentiles) in opposition to God in 1:18-32 (Perspectives Old and New on Paul, 387). Westerholm may well be right, but I think a 5th option--really a variation on Moo--is more (or also) correct.
• (5) According to Keck, “This verse does not summarize what Paul had said in 1:18-2:9; rather, it interprets what he had said by disclosing its import: The plight of the Gentiles and Jews is the same because what will count on Judgment Day is deeds” (95).

I suspect that Paul’s accusation—even though it is addressed to individuals and initially focused on establishing God’s impartial judgement—is meant to have illustrative force: Paul wants his audience to recognize themselves (or better, their pre-Christian selves) in the description and recognize their need. Paul's statement of the import of chapters 1-2 adds a new, previously unstated premise: "the problem with people is not just that they commit sins; their problem is that they are enslaved to sin” (Moo 201).