That dosnt look like a disagreement, it looks more like a misunderstanding. For two and a half chapters Paul describes mankind knowing the. truth of God but suppressing the truth I in unrighteousness, Jew and Greek alike judge under and apart from the Law respectively. Romans 3 I'd a transition marked by two words, ' but now', and what is reveal now is the righteousness of God in Christ which is by faith. What Red was pointing out is atonement is only mentioned in Romans in the 3rd chapter. There is no mention made of being a slave to sin unless you are simply projecting something you think is related to Romans 6. The blessings of those forgiven by God's graces occupies the content of the 4th chapter and chapter 5 is simply a contrast between being in Adam and being in Christ.
Atonement is a supreme Levetical event under the Mosaic Law. The word in chapter 3
What it says is that in Adam all die in Christ all are made alive. It does say that in Adam we are all under the curse of sin and death, it does not say that all are in Christ. Quite the opposite, Paul is clear that you are only in Christ by faith, and you are in Adam by birth. A distinction you appear to find elusive.