First, you are wrong about my system of morality (and I should know, it is my system of morality). I have a strong sense of moral obligation. It is kind of annoying for people to think that just because I don't believe in a Supreme Moral Truth, that I can't be a moral person. This is very clearly not true.
I assume you believe (as I do) that we didn't come from a creator and humans weren't made with any specific purpose. We evolved out of natural processes. As part of this process of evolution, we developed as social creatures. And as part of being social creatures we learned social skills; among these are language and moral values.
It is also true that among different groups of human beings, human traits like language and moral values developed in drastically different ways. All humans have a language, the languages are different. And, all humans have a moral code, but the moral codes are quite different). You can no sooner say that one societies moral code is superior to another's as you can say that one language is superior to another.
Where does this objective morality you insist exists come from?
Certainly this morality doesn't exist outside of human society. Animals act in ways that you would find immoral all the time (from child neglect, to rape, to vicious wars to murder of sexual partners).
I submit that morality doesn't exist outside of human societies. And therefore there is no objective way to judge between the morality of one society and another.
You are insisting that there is this "objective morality". But as the Universe doesn't care if humans live or die or suffer or prosper... where would this "objective morality" come from?