Escaping (note present tense...a work in progress ) the b/w JW mentality in which I was raised is one of the most challenging (if not the most challenging) thing(s) I've ever faced. I won't fool myself into thinking that I fully understand the answers that I think I have, but "the discovery is in the dialogue," so here goes.
I'll start here with a quote from An Introduction to Early Greek Philosophy (pp. 243-4):
The Transmission of Arete
How do men acquire this knowledge of right and wrong? You might as well ask, says Protagoras, how they learn Greek. They learn it when they are children--from their parents, from their teachers, from the magistrates, in short from everyone:
"As soon as a child can grasp what is said to him, his nurse, his mother, his tutor, and his father himself vie with each other to make him as good as possible; and they teach him with regard to every action he performs and every word he speaks that this is just and this is unjust, this is good and this is bad, this is holy and that unholy, and that he must do this and not do that. If he obeys willingly, well and good; if not, they straighten him out...
Afterwards they send him to school, charging his teachers to take more pains over the deportment of their children than their letters or music lessons. And the teachers do take pains over this, and when the children have learned their letters and are ready to understand the written word as formerly they learned the spoken, the teachers set the works of good poets before them and make them learn by rote--poems in which they meet with many admonitions and many stories and praises and eulogies of good men of old, so that the child will be inspired to imitate them and long to become like them...[other examples]"
In all these ways society takes care to see that its values are perpetuated.
...
One difficulty, however, remains. Protagoras seems to assume that the ideas of right and wrong which society implants in us by these methods are correct. No doubt they seem correct in the eyes of the society which inculcates them. But the question before us is not whether they seem right, but whether they are right...we know from other considerations what answer Protagoras would make to it: if the values of a society seem right to it, they are right.
This lays the groundwork for "subjectivism," and incorporates thoroughly debated and, imho, compelling evidence from epistemology and existentialism.
For myself, this has led to a strong conviction in "to thine own self be true."
There are numerous ramifications of this subject, including what might end up being "Part 2" of this thread: "Of all things the measure is man: of existing things, that they exist; of nonexistent things, that they do not exist."
Craig