Natural law is not arbitrary, physics is not arbitrary.
I am not a list of animals that engage in cannibalism. Cannibalism, among humans, has been demonstrated to have negative effects biologically, psychologically, and sociologically for a start.
You seem to be mistaking philosophical morality with religious morality. This is a conflation, used by priests historically, to confuse their subjects into believing that they, the priesthood, have the 'real' truth. There is nothing arbitrary about the natural function of the universe. Opinion has nothing to do with it. School testing has nothing to do with it. The word 'fail' is not solely used to describe the lack of expected performance at an arbitrarily created human test. If one walks along the edge of a cliff, with the aim of not falling, and fails to keep from going over, then correct philosophical morality is not achieved. Gravity is not arbitrary, and if the goal is to get somewhere, while not dying from a fall from a cliff, then the mark is set at not walking off the cliff.
Physical reality has no interest at all in human opinions, taboos, or justifications. No arbitrary human opinion will ever transmute a single atom, let alone mitigate the effects of misfolded proteins resulting from cannibalism in humans.
We must not confuse the state and function of the natural universe for the commands of humans or gods which no one has ever seen, or we may as well elect representatives from a pool of ghosts.
Well thank you for the conversation but I think this conversation is over.
What part ended it the logic or the facts?
I've had similar conversations with many moral relativists on Steemit, you do not strike me as one of those. This knowledge was a little weird to get my head around, given my deliberately stunted American public education all those years ago, but has been more useful in sorting out the truth of things than anything else I've learned before or since.
You do seem genuinely curious, not like the trolls I sometimes battle. Since you are done, let me leave you with this, the Trivium and the Quadrivium are an excellent place to start. Beware of the manipulations of the Trivium, for example the Neo-Platonists and the Prussian school. They altered it to create a theistic, authoritarian control mechanism, not to empower the individual with the knowledge needed to navigate this world ourselves.
Good luck. It's a turbulent world.