It's really remarkable how powerful that myth of romantic love as the basis for marriage has become, especially given how many people have the experience of "falling in love" and then falling back "out of" love again. I think that "romantic love" has power because it stands in opposition to more practical and less individualistic bases for marriage (e.g., marriage as an economic arrangement largely influenced if not determined by parents or other members of the community).
It's stunning, really, to think about basing what is, at least in the contract, expected to be a life-long commitment on an emotional state, given that emotional states are fluid. That said, there is no reason why polyamory couldn't also make use of some parts of the romantic myth while ditching others.
The romantic myth as currently held contains at least two parts: one is the "falling in love" part and the other is the "you're the only person for me" part. Poly culture could, I suppose, keep the first without the second, as many individuals already seem to do in practice if not in their belief systems.
I think my own hopes for a poly culture (not one that mandates polyamory but one that supports polyamory as a valid option and that incorporates poly households into its institutions) would be on that also challenged the romantic ideal and created new cultural understandings of love and intimacy, ones that blended individualism and community, and ones that blended emotions and pragmatism. I think such understandings of love would ultimately serve people as they try to negotiate and sustain committed relationships in a way that our current romantic myth cannot.
...because public space really matters!
Elizabeth