While many people would love to be able to determine law based on their own beliefs of right and wrong, there is no way to do so entirely. There will always be someone whose views will not be the end result, someone will always have an opposing view. Many times lawmakers endeavor to create legislation based on a moral obligation, but these laws are rarely useful in all situations. There will be a time where the moral context of the original case is not relevant to the new situation.
There is also the question of whether natural law actually exists. While positive law can exist even when unjust, it is not enough to be just in order for natural law to exist. There must be some measure of factual existence. A standard that was true according to values and that was not a part of a prescriptive system would simply be morality and law would lose its certainty. The Nuremberg Tribunal is one of the few cases of natural law where the court sentenced Nazi leaders for obeying positive laws that were unjust. They violated natural law by following positive law. The Nazi leaders were condemned by the court for their acts of atrocity.
Some have argued that positive law comes from natural law. For many this would be ideal. Cicero explains that the four basic categories of law—labor, property, self-defense, and family—are based on basic instincts such as self-preservation and procreation. This opens man up to a political community with its fundamental standards. This is just an example of how natural law might influence the comprehension of positive law. Nonetheless, this does not conclude that natural law is relevant for a positive law system.
Natural law is a system dependent on the inclinations of human nature, but what are those inclinations? How do we determine their ability to produce a just society? If we believe what the Bible says in Matthew 15:19, then there is no way that human nature should be the deciding influence on law. Matthew 15:19 says, “For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false witness, slander.” Certainly, actions such as murder and theft are fairly common, so we cannot conclude that human nature is against such things. There is also, however, a desire for justice. There is a calling for the people to be heard, judged, and acquitted. The problem is using the system to be fair and to represent all citizens in a way to which they are entitled.