I've had conversations with friends and others about defining what love is, inside and outside workshop settings. My experience among my mono friends is that it's rarely qualified as loving one special person exclusively. That usually only comes up if there's a comparison somewhere in the conversation between monogamy and polyamory. And if it was qualified that way, my answer to that would be "Great, that tells me *how* you love. Now let's talk about *what* that love is."
The same thing among my poly friends. I can't say I've ever heard a person define love itself in terms of having to love more than one person. The same differentiation is there. That talks about how, not what.
(plus, I've never read Heinlein and can't say I'm a huge fan or run among crowds that are huge fans)