Whether you call it natural law, or socially evolved conduct that has benefit for harmony and society, I think the real issue with this is that it exists, but we haven't really agreed on a legal definition.
Basically, we have been appealing to human nature and a higher power as a natural law giver, when the reality seems more and more to stem from social development, and the core things that disrupt society that everyone is expected to have adopted.
Most of it is universal, but look at an idea like 'common sense'. The diaphanous idea of all of the things people should simply know from existing as a human being. The reality of it is that we adopt values piecemeal throughout our development, hence why kids can seem to have no consideration for the world around them, but grow into thoughtful, productive members of society.
That considered, if we actually drill down to what is naturally beneficial to society (like not murdering, stealing, imposing your will on others save to prevent them from imposing their will on you), then the picture becomes much more straightforward.
So, yeah, natural law exists, but we haven't really defined why it exists, we haven't delved into what makes these things natural laws.
Whenever we argue about moral good and evil, we implictly appeal to natural law. We expect each other to practice charity, justice and not to lie, steal or cheat. Whenever a person is wrongfully deprived of their freedom and dignity(e.G. Raped or enslaved), there is a moral uproar. And we expect others to know these laws and follow them. Even if we deny natural law in theory, we appeal to it in practice.
Natural law plays an important part in many idealogys, some include demagogues, religious fanatics, political philosophers, even Hitler did so. Murray Rothbard, a political theorist who played a part "in the development of medern libertarianism", states that "Natural Law theory rests on the insight.... That each entity has distinct and specific properties, a distinct nature", which can be investigated by man's reasons" (For A New Liberty , p25). This procedure of thinking originated from Aristotle and has never been used in science in over 300 years, Science is based on experiments and creating theories around them to explain what occurred in the experience. Rothbard invents these "definitions". Methods like these were used by medieval churches and lacks any scientific method. After lines are drawn from defining the "natures", Rothbard then draws "Natural Rights and Laws" but these laws are violated in nature. Natural Laws like gravity cannot be violated so it does not need reinforcement but "Natural Law" in justice does not exist as they need to be enforced by institutions and societies. Natural Law also differs from society to society, some believe that Cannibalism is normal, others believe that killing a dog is more in humane that a pig even though pigs are more intelligent. Natural Law is created by society and is enforced by it as Ayn Rand, the developer of "a philosophical system called Objectivism" , claims that "the source of a man'a rights is the law of identity. A is A and Man is Man" defines "Man" as an "entity of a specific kind- - rational being" But this form of thinking does not account for "irrational behaviors" which is also produced by nature. Which would mean that A cannot be A as they are not human, thus denys the law of identity.