I identify with your perspective, however you conflate christian religion with christianity. Religion is what you get when grifters try to "save" people by collecting a tithe and form a government and law to "make them christian." The role of religion is to preserve and transmit the good news, but its also a snare for those that don't recieve the good news and instead make the promulgator into an idol.
Regardless, i don't think the golden rule is learned, instead i believe its a rationalization of the empathy instinct. This is what is meant by the Law is written in men's hearts.

Rom 2:14-15 KJV For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves: Which shew the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another;)