And ye shall know the truth, and the truth shall make you free. However, the conscience can be improperly educated with a defective standard. Hence, cannibals can kill and eat fellow humans without a sense of guilt. Remarkably, they instead might be praised by their consciences for practicing cannibalism.
Christians realize that there is a moral standard that is superior to personal and community ethics.
The community standards of Nazi Germany that allowed the holocaust to occur are viewed almost universally as violations of a superior ethic. The Bible is the final, absolute standard authority for all people, irrespective of whether they realize it. In his mind, there is an absence of a perception of a moral standard. Ordinarily, this condition is confined to small children, other mentally unaccountable souls and animals. Of course, young children, mentally deficient persons and animals lack the capacity to perceive morality.