However, the point of mergence between the two theories has been given a name for itself and it is known as the Overlap Thesis. Overall, the natural law theory of law is used to refer to the analysis of legal systems and philosophical issues of law.
Among those who sought that natural law has no valid grounds is Leo Strauss who was convinced that it has to be refused on the premises of history and of the differences between facts and values. To most of those who oppose natural law, human knowledge and thought is characterized by the historical interpretation and history is time-bound and thus unable to encompass something which is eternal. Another reason natural law has been criticized is because of its ontological and epistemological suggestions. In regards to the former, it has been noted that no matter the way reality is perceived, whether from a theological point-of-view, cosmological, philosophical, etc. natural law, most of the times, deducts the nature of things as something subjected to a course of action which leads to something that exists because "it has to" not because "it does." and, from an epistemological point-of-view, the premises that the actions are knowledgeable to any individual, through whatever means, is not something foolproof.
Natural law has been attacked from various points-of-view. Topics pertaining issues of ethical imperialism, political utilitarianism, jurisprudence, positivism and historical materialism (Karl Marx) have criticized several features of natural law. Thus, one of the objections on natural law is that "it serves no useful purpose," that is to say, specifically in regards to natural rights, that they are of no use because a Natural Law concerning murder will offer no guarantees of protection from murderers, something L.A. Rollins has touched on in his book the Mith of Natural Rights. To exemplify his notation he addresses the Jewish topic and raises the issue of their natural right to life which was dismissed completely under the Nazist regime. In this respect, he considered that natural rights hold no validity as "protective devices" since so many Jews were killed.
Another objection sustains that "such a thing as natural law cannot exist" because the very issue of natural law is something obscure and, going back to what I was saying in the first few paragraphs, that natural law as a moral theory is subjected to only a quantum of certainty, this definitely applies to the aforementioned objection. Followers of this criticism are inclined to perceive natural law as merely a descriptive concept, but this vision would ultimately dismiss that "natural rights are normative facts," not something mysterious. It has also been argued that the morality ascribed to the natural law is in fact an act of manipulation, that is to say, a tool for making people do what one wants, but such a supposition would not explain why people keep on privately pondering on moral dilemmas or make decisions that eventually are for their own good as well as for the good of others.
I have already mentioned that one of the accusations pending on natural law is also its lack of scientific basis and the fact that a lot of what constitutes natural law is neither verified nor tested. Thus, there is no proof, nothing to justify that what one knows is true. Modernist approaches have looked at the moral truth derived from natural law as something emerging of reason rather than of faith. But the idea that some concept regarding natural law is self asserted led to hostile reactions. Another argument in favor of those opposing natural law is that, since it has not gone unchallenged and because, in cases of something truthful all people agree, but so many discrepencies are to be found in regards to natural law, the conclusion is drawn that such a concept is non-existent. In favour of the advocates of natural law, it can be said that they alone acknowledged that the theory is to be constantly discovered.
Rothbard, Murray N. The Ethics of Liberty. New York and London: New York University…