Emotions vs. Rationality
So here's a poser for you, that I've been thinking about quite a bit lately.
Background: my wife is monogamous, and I have had poly feelings for a very long time, and finally figured out that just admitting that I'm polyamorous (and telling my wife about it) relieved a hell of a lot of stress.
Anyway, there's a wealth of writing out there that advises about how to help your mono partner feel secure, and how to help your mono partner deconstruct and handle jealousy. The advice generally boils down to using reason to conquer fear (e.g., "No, he's not actually going to leave me for her."). In a sense, you help your partner tell herself not to be jealous.
What would you as a poly say to a mono who responds, "Well then, why don't you just tell yourself not to fall in love with anyone else?"
(This has not actually happened in my case, but I can see how it could, and I don't doubt that it has happened with many couples who were exploring opening their marriages.)