They also give excuses such as "God is a loving God so He won't judge us." "Sin isn't so bad if we can learn valuable lessons from it; or we need to stay in touch with the culture around us." "Our sin would amplify God's grace, therefore the greater the sin, the greater is God's glory." Sinners will use any feasible logic to justify their lustful desires even if it means using God's own righteousness for an excuse.
It's far too easy to take God's grace for granted, but God can't overlook sin. Sinners will make many excuses and justifications for living in sin, but no matter what, all will be held accountable to God. The gospel should make us more accountable, not less accountable. Those who know the truth have a higher responsibility for their actions.
SIN OR SANCTIFICATION?.
The early churches were still developing and on the receiving end of God inspired doctrinal truths. Paul knew the mind of his readers. He understood that some men would pervert the truth. He knew Roman inclinations, philosophies, strengths, weaknesses, and culture. Paul states the devilish proposition beginning in Romans chapter 6 "What shall we say then? Shall we continue in sin that grace may abound?" I would not be surprised if the question were presented as direct quote from Satan, but Paul plays devil's advocate. He drags the thought from the lustful mind of man which results in a mandatory answer, a forced response to an errant consideration.
Romans chapter 6 is a rebuttal to those who would see grace as a way to justify their sins. Paul's immediate response is "God forbid". Other similar translations would be "Of course not!", "By no means!", "NOT!", or "No way!" We should continually conform ourselves into the image of Christ. Prior to salvation, we loved darkness rather than light and we avoided the light because of our evil doings (John 3:20). The pre-salvation state was void of any desire or capability for sanctification.