This is more of philosophic approach than a literal one. This is another one of those conversations that tend to spring up at one or two in the morning when the shift gets boring.
To start with, let's get rolling with a quote from Socrates "Before we begin talking, we must decide what we're going to talk about."
It all started with this simple, unassuming question: "What is a conscience?"
You would not believe the chaos that ensued.
After I stepped back and took a close look, I realized that our consciences tended to follow what was morally good for a particular society, as well as what our parents tell us is right. For instance, it is highly barbaric for a man in Western society to keep his wife locked away or beat her for simply glancing at another man. However, in Islamic areas, this is the traditions that they have followed for centuries.
So, by their morality, they have done nothing wrong.
I believe what most people call their "conscience" is simply a collection of what society, and your parents, have told you. Since I come from an extremely conservative home, sex outside of marriage is highly frowned upon and believed to be a sin.
But for someone from a more liberal household, sex outside of marriage is nothing wrong.