It's a false premise to say that most monogamous people have chosen monogamy. Most people belong to the religion they were raised in...because that's what's familiar. That's the milieu they grew up in, and, for better or worse, they're just continuing the pattern. Until this traditionalist mindset is shaken loose, you would likely try from reflex to impose notions onto nonmonogamy that are not only untenable in the new context but spell sudden and messy doom even in situations that otherwise could be worked out.

Polyamory: Roadmaps for the Clueless and Hopeful: An Introduction on Polyamory