In fact, it seems to me that Paul is trying explicitly to keep this from being the main point, lest we base our condemnation first on our individual sins, and then base our justification on our individual righteousness. He is trying to avoid that mistaken view of justification. That is, death came to all, but it was not owing first to their individual sinful acts. For example, infants died. But, even though it is a subordinate point in this passage, it is here.
All people become sinful in their nature and in their behavior.
In other words, something happened to us in the sin of Adam that altered our human nature. We are by nature unrighteous. That is the condition of all human beings since the first man sinned. So we have seen two things that need a remedy. One is our sinful nature that enslaves us to sin, and the other is our original guilt and condemnation that is rooted not first in our individual sinning but in our connection with Adam in his sin.