Polyamory is differentiable from some other forms of nonmonogamy (including adultery) in that it is future-oriented. Poly relationships are not located solely in the moment, but have intentions (though perhaps tacit and vaguely defined) of at least adding to a base of experience possibly so far as signifying a life-long and emotionally attached commitment.
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 spel sudden and messy doom even in situations that otherwise could be worked out.