The very fact that modern philosophy is asking this question shows that rationality, pursued in the abstract, leads to self-destructive madness. The United States was created on the notion of natural law, that there is indeed something more important than the arbitrary decisions of despots. Instead of fretting whether this natural law (and hence basic human rights) even exists, philosophers should be engaged in an all-out struggle to castigate tyrants for replacing the natural law with common law, as has been done in the case of the Drug War. The Drug War is the triumph of contingent common law over natural law, imposing arbitrary limits on a human being's right to Mother Nature's plants, and thereby massively incarcerating minorities and keeping a myriad of godsend psychoactive plants not merely from "druggies" but also from depressed patients and soldiers with PTSD, even blocking research on such godsends. So if we want to see the results of considering morality to be illusory, we have to look no further than America's overcrowded prisons or the record-breaking instances of depression in America, or the Drug War-created violence in impoverished cities. Please, philosophy, stop counting angels on a pin and start dealing with the real world: take natural law (and hence human rights) as a given so that you have a leg to stand on when confronting tyrants such as Donald Trump, who now plan to start executing the minorities that the common law has allowed America to throw in jail for the last 50 years.
Meanwhile, if you're starved for good philosophical topics, how about the following: Resolved: that the Drug War is the enforcement of Christian Science Sharia?
The natural law is premised on the idea that an ultimate morality exists. Once we start questioning that assumption, then any tyrant can justify any action based on force and expediency. Slavery, under such a view, is never fundamentally wrong, but only wrong insofar as it does not prove expedient and/or is incapable of being maintained by force of arms.