No doubt there is plenty of room to argue about the best system. But to say that our current system is COMPLETELY arbitrary, and that fairness is WHOLLY irrelev

No doubt there is plenty of room to argue about the best system. But to say that our current system is COMPLETELY arbitrary, and that fairness is WHOLLY irrelevant to the discussion is dangerous hyperbole. It would certainly be unfair, even cruel, to restrict everyone's income to the exact same amount, regardless of what they do. It would also lead to extremely low productivity. The fact that we don't do that isn't arbitrary. Our current system has evolved, imperfectly, from common ideas about rights and incentives held by various thinkers throughout human history. Let's not talk as though it were the first thing vomited out of a random law generator.