This theory is rather thoroughly explored in Sex at Dawn. Of course it began long before medieval times. It's quite obvious in the Bible for example, especially the Old Testament, in the laws, and in the historical books where patriarchal Yahwist tribal lords strove so mightily and violently to overthrow goddess worshipers (Asherah and Astarte).
For more help at reading between the poetically politically slanted lines in the Old Testament, read When God Was a Woman, and The Hebrew Goddess, both scholarly books.
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
There's no lying in polyamory!
I'm a 58 year old woman with 2 partners:
miss pixi, my live-in gf, 36 (together since Jan '09)
Ginger, bf, 61, married, lives nearby (together since Jan '12)