The fact that you “need” or “don’t need” something is utterly irrelevant to whether it actually exists.
So let’s assume “needs” means “is logically necessary.” The problem with ethical systems based on personal or even group morality is they are utterly subjective, with no reality beyond the believer’s skull. Sure, you can argue that the ethics are necessary to the workings of a stable society, but then someone comes along and says “Screw you and the horse you rode in on. I find it more rational simply to take what I want. I don’t care what you think and I and my followers have enough power to smash you if you oppose us. In fact, we fully support your ethics because it creates a pool of potential victims for us to exploit.” Your move.
It’s conceivable that, had Germany won World War II, we might have a world where total obedience is the ultimate good and the extermination of the Jews was a necessity. For a really creepy and stomach-churning alternate world where morality is totally based on might, read S.M. Striling’s Drakian trilogy, where he posed the question “What if history turned out in the worst possible way?” In Stirling's alt-world, 90% of the population are slaves (“serfs”) over whom the freemen have absolute authority, and they kill as casually as you’d swat a fly.
Consider the argument “If morality exists, there must be some deep cause that makes things moral or immoral.” Before you dismiss it out of hand, substitute “mass” for “morality.” And the EU says “Here’s ten billion euros to prove it. Knock yourselves out.”
Note that at no point have I invoked the supernatural. Whatever makes things moral or not could be as deeply rooted as, say, conservation of energy, and we need not invoke the supernatural for it.
