There is objective right and wrong
There is an objective morality, I would go far as to say that I agree with St. Paul when he talks about each human has the law written in his heart. Someone may say that morality is relative, until something happens to them. A man may think that it is ok to steal as long as he is not caught, but if something of his is stolen, then suddenly it is wrong and he wants the wrong doer punished. Men may pillage villages and rape their enemies and believe it is alright, but they know that it would be wrong if it happened to them...their wives raped and children sold into slavery.
To steal, to take another wife, to kill (by that I mean murder not self defense), to hate another because of their skin color or religion, all know that it is wrong, even when those who commit these acts have good reasons (in their own minds) to commit them.
The Golden Rule points to an objective morality, to treat others as we would want to be treated. To live that out takes self reflection and self knowledge.
So yes there is an objective right and wrong, just look at how you would want to not be treated, used, abused, stolen from, your loved ones hurt, or yourself murdered. When we do wrong we know it, we know sin when we commit it, and when it is committed against us.