Why should it be justified at all? I feel like you're coming to logical conclusions based on all the wrong questions. ;-)
Edit: Oh, and if you're actually interested in wasting some time on a little literature you might enjoy some Alain de Botton; he's a logical ninny that's written some good stuff on relationships in a weird way of combining a novel with light philosophy. On Love is probably better than The Romantic Movement; though the latter paints a prettier picture of romance.
I said that, as we all know, it hurts people. If you can't justify good reasons to do it anyway, or come up with an argument it doesn't actually hurt people, then it's a bad idea.
Happiness, and success are a perspective, not an objective reality. Importance is synthetic. Freedom is just a macroscopic view of determinism.
If you can find a way to be happy with or without relationships, you win. People seem to have succeeded and failed with both strategies.