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Morality can not be an agreement on values, morality is a concept, it does not exist, is subjective.
The same goes for values, values are subjective, a concept, they don't exist.
You can't have an agreement on things that are concepts and are subjective, for an agreement is also a concept, and is subjective.

You can only have an agreement if you determine the words agreement, morality, values. And both agree that there are such a things as morality, and values, and agreement, in other words, sort of, make them objective. If one of the human in the agreement sees everything as subjective, there is no agreement.
How could there be.
An agreement comes with determining words,
An agreement in the form of a contract comes with, keeping your word, how can someone keep their word if they are not willing to determine what the words mean?

The first title was to be "morality does not exist" but i ended up with just saying it is subjective. i get what you say though.