Cephus
Relentlessly Rational
Agreed, but not necessarily to the individual. The standard is enforced by society as a whole. Certain things are considered immoral by the community, and the community gives itself authority to enforce these morals through various tools.
Sure, morality is something that is adopted by societies and taught to individuals within those societies. That doesn't mean that the morals adopted by various societies are necessarily correct or factually true, and we know that they do change over time. What we believe to be moral today will invariably change in the future and they'll look back at us and think we were immoral. How anyone can make a case that this is objective is beyond me. The fact remains, nobody is making a case, they are just claiming it exists.