The content of conscience depends upon knowledge. When what you know is wrong, you may have a good conscience about it though being in the wrong. In some tribes, the power to seduce women is applauded. Without the light of the gospel, fornication is no sin there. A man can therefore be fornicating with a good conscience.
There was a time we did not see what was wrong in divorce and remarriage. That was based on the light we had on the issue at that time. But as we got more light, we have had to take God’s position in the matter.
There are traditions where an only girl to the family is not allowed to marry. She is allowed to produce children with men out of wedlock. Such a girl could do so with a good conscience.
In other cultures a girl must prove her fertility by becoming pregnant at home. This qualifies her for marriage. Hardly is the act of producing her bastard called fornication and scorned. A sister told us that until she met us, she never thought that fornication was sin. She knew the problem was with adultery.
Paul persecuted the believers with a good conscience. It never occurred to him that he was doing wrong until he heard the voice of Jesus. He had a clear conscience in the wrong. And after that he walked with a clear conscience according to the light he now had. He himself says, “…My brothers, I have fulfilled my duty to God in all good conscience to this day” (Acts 23:1).
Before conversion and even after conversion, conscience judges and passes verdict on the basis of its knowledge.