Here's a video by Dan Savage (a very successful love and relationship columnist who writes "Savage Love" -- which is often hilarious) and he speaks about why he things monogamy is ridiculous. I agree with him, but of course, I have penned other articles on Polyamory so I have certain leaning and he's really preaching to the choir. Basically he says: men have long been non-monogamous for most of recorded history. But women were treated as 'property' and tied to a single man so that he would know who his heirs were.
Then over the last 60 years or so women gained more right and the idea of marriage for romantic love as the primary reason for marriage came into its own. But instead of granting women the equal rights of men -- we went the wrong way and shackled men with the limitations we had previously placed on women. With disastrous results.