"What is truth?"
Pontius Pilate
Morality is a form of cooperation, but it evolved to help individual groups of humans. It can be applied between groups of humans, but that is not required.
For example, codebreaker believes that only creationists are going to heaven. In fact, he revels in his fantasy of Gould burning in hell. Yet, he would be horrified by the idea of himself burning in hell, with his skin blistering and flesh melting for all time. He can do this because he only applies his morality to his group of people, the creationists. Anything is ok for anyone else. This is exactly what Genghis or Hitler did. Morality, in humans, only seems to apply to the group that you are in.
Is this good, or just? No. It is just true.
I'm tempted to ask, "what truth?", but instead I will simply ask if you are presenting your claim of "society says" morality as descriptive or alternatively, as normative? Morality itself involves notions of "ought" and "should", not merely with what "is", in a descriptive sense.
There are numerous problems with understanding normative morality as a "society says" morality. For example, it becomes impossible to judge or critize another society, if there is no moral law above society. Then you've got the problem of which "society" to obey, the population at large, or just the people with the power to rule? If people have a moral obligation to obey whatever their society presently says to do, then for example, Germans in the Nazi era would have had at that time a moral obligation to participate in the murder of innocent people. There could never be any such thing as an immoral law. If courts and laws define what is moral, then neither laws nor governments could ever be immoral, even in principle, which renders incoherent the concept of moral reformation. Moral improvement under such a philosophy actually becomes unethical, an obvious absurdity.
Cordially,
Speaks volumes about the person saying it..