The Argument from Queerness

One argument against moral realism says something like: Moral properties are so queer! They'd be completely unlike anything else in the universe in terms of their properties.

But I don't really understand the force of this argument. Quarks (or whatever fundamental particles are) are entirely unique too. They're unlike anything else in the universe. Sure, they might be more numerous, but that's hardly relevant.

So why would we think that the uniqueness of moral properties makes them unlikely to exist? Fundamentally, the universe must consist of various unique kinds of properties and entities. That's what makes such entities and properties fundamental.