dominated by sin

We are not dominated by sin. John Piper, in Bloodlines, explains that dead people are not dominated by sin:

Paul answer this distortion of his gospel of justification by grace alone through faith alone? The answer is devastating to a superficial view of Christian conversion that reduces it merely to a “decision for Christ.” Here is what he says: “What shall we say then? Are we to continue in sin that grace may abound? By no means! How can we who died to sin still live in it?” (Rom. 6:1–2). The point is that when we put our faith in Jesus, we are united with him so that his death becomes our death and his perfect life becomes our perfect life. His death and righteousness are counted as being ours before God.

Paul says that in baptism, which happens “through faith” (Col. 2:12), “we have been united with [Jesus] in a death like his” (Rom. 6:5). This union with Christ is how we experience death. “You have died, and your life is hidden with Christ in God” (Col. 3:3). “I have been crucified with Christ. It is no longer I who live, but Christ who lives in me” (Gal. 2:20).

So two kinds of things happen when we trust in Christ and are united to him by the work of the Spirit. One is that we are counted as having died with Christ so that we received the punishment of our sin in his punishment. God condemned our sin in his flesh (Rom. 8:3). The other kind of thing that happens is that our old unbelieving, sin-loving, Christ-neglecting self really dies. That is, we are not just forgiven for our sins, but we are given a new identity.

This is how Paul responds to the question: Shall we sin that grace may abound? No. The self that loves sin has died. The new self is not yet perfect. It sins. But it does not make peace with sin. It hates sin. It confesses sin and makes war on sin. That is the background of Paul’s question, How shall we who died to sin still live in it?