If you can produce another candidate, by all means feel free. You can assert that magical orcs and goblins invented it, but it would behoove you to produce an orc and a goblin in that case. I, on the other hand, can provide evidence of humans, and the great works of literature we create expounding on morality and ethics.
I don’t think you understand the structure of a circular argument. I made no such assumption. I simply am following the evidence where it leads. I am not arguing that nothing exists outside our universe, just that we have no evidence of it, at least not yet. Since we have nothing to indicate any entities exist outside our universe, the correct, default assumption is they have no bearing on things such as morality and ethics.
Hubris, huh? How about if we just don’t consider fantastical, magical possibilities until we see some credible evidence to suggest they might be real. Extraordinary claims require extraordinary evidence and all that. Otherwise, I will have to note the amazing hubris you display by dismissing the fact that invisible pink flying skymonkeys are really inside of Barack Obama’s brain controlling his actions, while the Flying Spaghetti Monster and Zeus were dancing together at the Inaugural Ball last night. I mean, logically you can’t say it didn’t happen, right?