It seems a little odd that you state that we’re “getting into a tight little loop” by referencing “morality (or making an appeal to authority),” and then you go on to create an even tighter (or slacker) little loop by referencing some moral rule or other.
It isn’t clear to me that simply universalizing actions actually determines what is “good” in any insightful way, so much as define the “good” as what good or reasonable agents would choose to universalize or engolden.
Either way we are left with the question of what it is that makes the choices that “good” people choose actually good. Seems you still end up with a Euthyphro type of dilemma – Is the pious loved by the gods because it is pious, or is it pious because it is loved by the gods? – except that “the gods” are replaced by “rational” or “good human beings.” Is the good loved by good and rational human moral agents because it is good or is it good because good and rational moral agents love it?
Rules and principles don’t so much uncover the nature of morality as provide a conceptual system by which to try to uncover or understand it.
Seems to me that no morality is possible without a teleology or a fundamental purpose for which things (including humans) exist and that is not possible absent purpose, significance and meaning being inherent within the fabric of being or existence itself.
If existence reduces to pure purposeless matter that exists as brute fact for no reason and without significance, morality is fundamentally groundless and warrantless. Oh sure, we can pretend or imbue our existence with some sense of value, but in the end that value is merely grounded in human imagination and desire. Change the desire or imagination and voila, a completely different morality is conjured up.
If a large number of humans contrive a society based upon rape or pillage, those become the standards for their behaviour. If another group contrives a society based upon private ownership or enterprise, then those become the standard by which their morality is weighed. There is no way to rate one group as having a higher morality or standard than the other because the standard is grounded merely upon human determinations. Sure, you might be able to persuade some group or other to agree to a different standard or morality, but then you are not resolving which is better, you are just compounding the issue by multiplying moralities.
Morality has to be based within the nature of what it means to exist as moral agents and sourced in a proper understanding of quality or meaning regarding that existence or it is without ground or foundation. Existence itself has to ground morality or it is merely contrived.