Gaudium et spes is not wrong!  Ratzinger [and you assume] that people don't know the moral law by choice.  The MORAL LAW that is being referred to is the Judeo-Christian moral law.  What about people who are NOT Jews or Christians.  And as each year goes on----there will be many more people who are NOT Jews or Christians.

Cultures, societies, and the primary unit of society----the family----have more to do with people knowing or not knowing the moral law.