People, as social creatures, naturally come together for the betterment of each other. Each individual functions better by being a part of a resourceful and supportive group rather than an uncooperative loner. As such, we would naturally form a system of laws to make the group function as best as possible. Eventually, these laws would be complemented with consequences for those who break them. This is all without a supernatural view of morality.
Keep in mind it's not morality that keeps people in order. Laws and consequences are what keep people in order. These laws and consequences evolve naturally as societies try to do what's best for itself. Unlike morality, these laws would have real-world consequences. And if there's some prevalent behavior that the society decides is harmful, then it will eventually be weeded out. As societies evolve, they will naturally discourage harmful behavior while encouraging supportive behavior without a supernatural explanation of morality. Why? Because it increases their longevity, which is something all beings naturally want.
The actions we label as "right" or "wrong" don't have to be backed up by some absolute & divine source of morality; instead they are backed up by what we, as civilized societies, have discovered to be what's best for people and our species. So when we say "unnecessary murder is absolutely wrong", we aren't saying there's an ever-reaching system that makes murder wrong. We're saying unnecessary murder is absolutely harmful to society, which is bad for everyone, and is thus a "bad" action.
That being said, I don't know of any evidence for a supernatural view of morality. We obviously don't need it to say that certain behaviors are "right" or "wrong". We can simply say that certain behaviors are bad for society, and it will have the exact same meaning and interpretation. Some people may ask, "why should people feel obligated to do what's best for a species?", but I think this is a really silly question; people will naturally want to do what's best for its species, and it's specific group because it helps each individual in the longterm. It's not that complicated.
It really doesn't matter if you believe absolute morality exists or not. You must agree that humanity naturally develops certain rules that are always considered "good" or "bad". Whether or not you call that "absolute morality" is purely based on semantics. But what gets me is people that believe absolute morality can only be explained using the supernatural. I do not understand these people.
