Are people without the law of Moses still guilty of sin?

Les explains that Gentiles who did not have the law of Moses nevertheless did by nature the things contained in the law, being a law unto themselves. Their conduct showed the work of the law written in their hearts, namely their conscience. Even without the Ten Commandments—thou shalt not steal, thou shalt not kill, and thou shalt not commit adultery—they had a moral system. Les illustrates this with Indians from the Amazon jungles who, though uncivilized and thinking nothing of murdering people, have within their own tribal community a moral code that would put America to shame. That moral code comes from conscience. Therefore Scripture says that even though they did not have the law, they were guilty of sin just as much as anyone else.