There is no right and wrong if it is relative.
There is only lawful or unlawful.
My argument is that first off there is no God, so no divine being established universal morality. Yet, you believe in a certain and undeniable moral code. So, where did that moral code come from? It came from humans and is based on reason. That's the only place it has ever come from and the only place it can come from. God did not stop us from living by the law of the jungle, we decided we liked it better being "civilized" and abiding by a common notion of morality.
When we discuss moral principles we do not just say "God said so" even though theists acknowledge that they cannot know the mind of God. So why don't we just say that we do what God says no matter what? Because we are rational, intelligent beings who interact with our world primarily through our mind. It is the human mind that shaped your reality...even the idea that a supreme being, the father of all fathers, exists. You moral code is glorious...and is the product of simple human thought.
I'm sure you're aware that modern Christians ignore, completely ignore and disregard moral concepts that were held near and dear to your faith as the word of God only a very short time ago. Why? Because the **** didn't make sense so it was rejected. Humans don't engage in nonsense, especially nonsense that isn't useful to our rational desires.