the nerd, as a comment on your first statement, isn't it because being non-monogamous is not seen as a viable option? its illegal if you want to marry more than one person, so how could anybody teach non-monogamous ethics?
btw, i agree with your statements.
A long-delayed reply to "How could anybody teach non-monogamous ethics?"
Teach non-monogamous ethics by omitting marriage from the course description, as my kid brother and his girlfriend 30 years ago omitted marriage from their lives. He is 66 now.
A belief that monogamy requires marriage exists only in the minds of people who long ago had the belief put there and who have not removed it.
Ditto for a belief that marriage requires monogamy.
My wife, who for several years had taught in a school system with a comprehensive sex education program that started in second grade, and I removed that belief. We spoke with two couple about spouse swapping and found that after a party we went home more turned on than we'd been when we went to the party.
Several years later we separated, not due to jealousy issues but because we had both grown up in old-world European families that discouraged talk because it interfered with work. We saw a counselor and after our divorce we both joined a large singles club. At its Sunday evening meetings we occasionally danced with each other, surprising a few of the club's members. About thirty years later in another state, we find that we live about fifty miles away from each other and have a long phone chat.
Monogamy requires marriage and marriage requires monogamy only in the minds of people who believe they do.
You could verify them. Rather easily. Will you try?