An instance where a critic takes an incident and transforms it into an absolute principle. The covenant in Genesis 9 are made with Noah, who existed much later than did Cain.
The blood-shedder must die
Genesis 9:5-6 - Whoever sheds the blood of man, by man shall his blood be shed
The blood-shedder must not die
Genesis 4:15 - If anyone kills Cain, he will suffer vengeance seven times over
Asking questions is very important. It helps us learn, understand, and connect with others. We must continuously question ourselves and others to verify we are on the correct path.