Caste system is Wrong.
Slavery is Wrong.
CO2 emissions are bad."
Right? All agreeing (almost)? Good.
Female Emancipation is right.
Democracy is Right.
Equal Opportunities are right.
Now I give you five minutes per point. Start justifying. If you do manage that (satisfying yourself in the process), kudos! You are not Sheep!
Social Morality is a statistical quantity that comes from consensus (of course). To arrive at at it, requires presence of a Mass Media, which can communicate advantages of certain policies and Horrors of certain customs before anyone can be made to distinguish Right from Wrong.
Mass Media is a 19th century invention Gentlemen and Ladies.
There is no way in hell, we can blame historical societies for being as they were i.e. different than today. Morality is not/can not be made Retroactive beyond a given period of time from whence the world differs in means of communication and knowledge.
If you are still applying it and passing judgments, you are not so smart (sorry).
The question is, are you still going to become smart or not.