Objective morality exists and the most reasonable explanation is an objective moral law giver.
One piece of evidence for God’s existence that is found inside our universe is the existence of moral laws. There is a standard that everyone is expected to live by and by which we are held responsible. We see this when we are able to judge another person for their moral actions and say that they were wrong. There are certain moral actions that are wrong for all people, in all times, and in all places. So, who gets to decide this standard? Can objective morality be explained while staying inside our universe? The problem is that staying inside the universe does not provide a foundation by which to ground objective morality. The only way this moral standard can be explained is by showing that an objective moral law giver exists outside of our universe. What are we left with if there is no moral law giver outside of our universe?
Nihilists have rejected the idea of objective morality and say that moral statements cannot be either true or false. This means that there is no good or evil action. Love is no different from rape. This view cannot be lived out.
Subjectivism (I say Relativism)
Others believe that there are moral laws, but that it depends on the individual to decide morality. This view is called subjectivism; the subject gets to decide what is morally right and wrong. In this view, one is unable to say that the moral action of another person was wrong since they believed it to be good. They best you could do is say that you don’t like what they did, but it is just your opinion vs theirs. No one is objectively right.
Society Says Relativism
Since many see the problem of subjectivism, they attempt to explain morality by saying that groups or cultures get to decide right and wrong. This would mean that you are unable to say that another culture or group is morally evil. In this view, it was wrong for other countries to judge the Nazis for morally wrong actions. They lived in a different society and were doing what was right according to them, therefore, they did nothing worthy of punishment. It also becomes difficult to know how large the group needs to be in order to change morality.
Since these proposed solutions seem to be difficult to define, some philosophers have based moral truths on human flourishing. But just like subjectivism, which person gets to decide what flourishing is? Why is flourishing the best standard for judging morality? Some people flourish while taking advantage of others. Are they wrong? Also, why is it that humans get to flourish? Why not another species? Should we be tried for speciesism for thinking we are better than other species?
Every attempt at explaining objective moral values while staying inside of our universe fails. This is why many choose to completely reject the idea of objective morality rather than trying to ground it in foundations that don’t stand. In order to have laws that transcend all people, we need a being that transcends all people. The best explanation for the existence of moral laws is that there is an objective moral law giver that exists outside of our universe.