Of course it can be applied. We know that those states and governments are wrong by the universal moral code condemning murder, slavery and genocide. We would have no grounds to condemn these things, if it wasn't for a universal moral code.
With that definition any moral code can he universal.
I can support legalized murder and condemn everyone who doesn't, therefore creating the grounds to condemn anything else.
Some religions practice human sacrifice, including of children.[1]
My opinion is we're better off arguing there's a better moral code based on a number of arbitrary parameters (freedom, resource creation, comfort, longevity, equality, merit, envy management, violence management, respect for tradition, respect of minorities, etc). I can't see how you can declare a universal code of conduct, I can see how you can declare a technocratic liberal one.
I'm not denying that civilizations use different moral codes. I am trying to say that we must have appeal to a universal moral code in order to judge whether a culture's moral code are in fact moral or not. This would apply to our own moral code as well as for those of other civilizations.
I am saying that if we are too say the Ancient Mesopotamians was wrong for sacrificing their children, we have to appeal to some kind of universal standard outside of them to do that. This logic also applies to the Aztec human sacrifice, and to the way the Nazi's treated the Jews. We need a universal standard to say they were wrong.
To make this more actual: You are advocating for a technocratic liberal moral code. Many people are advocating for a historic Christian moral code. How would you even start debating the Christians without appealing to a universal morality? You'll have to assert that your moral code is universal. If you don't, you have no basis to require other people to behave according to your morality.
If a universal moral code exists, it wouldn't cease existing even if 100% of people dissents from it. The whole point of a universal moral code is that it exists outside of us.
Of course it can be applied. We know that those states and governments are wrong by the universal moral code condemning murder, slavery and genocide. We would have no grounds to condemn these things, if it wasn't for a universal moral code.