It seems like the original author is ill-equipped to teach philosophy if he isn't familiar with the a posteriori state of morals.

He wants moral facts -- a priori moral guidelines that would exist regardless of the nation or classroom. There aren't any.

Instead we have moral assertions that are inherent in the social contract. While these have to exist for any civilization to exist, they are still only inherent to that state. Having a paved town and not murdering each other are super important for us to make progress. Nevertheless, that's not inherent in being alive -- it's inherent in not fleeing to the woods and never having a day job with other humans.

Don't steal, don't cheat, don't poison the well. It all makes sense when we each want to have stuff, each want to know the abilities of each other, each want to drink from the same well. It's obvious but not mandatory -- and the punishment for flouting such rules is some from of exclusion from society.

This is basic Rousseau, straight outta Hobbes as well -- Ethics 101. Nature is nasty, brutish, and full of disease-riddled insects. You want out? You agree to some stuff. That doesn't make those rules into facts -- just deep-down, well-tested opinions. The laws that come from these rules are facts, but they are also instantiations of opinions. It's much like turning pseudocode into code.

It's like how gravity is still a theory. We will never get to shake gravity's hand, but we'll also never get to escape it. Even in outer space, it will pull us around.