I'm poly because... I am. I think I am in a healthy relationship in large part because needs and desires are openly stated. I'm not sure that left to himself that monogamy is my husband's natural state, given his history. Setting the parameters of our marriage to allow other loves generally insures no cheating as I define it. Because to me, cheating is not getting one's emotional or physical needs met elsewhere -- it's the hiding and the lying when doing so. It's deliberately abusing the trust of the relationship, and feeding ignorance to those who need knowledge. Oh, it could still happen. People do the damnedest things for the strangest reasons at times. But I think the odds are improved.
And well, I don't see myself as monogamous. Early on I realized my ideal is a triad, preferably one where everyone loved each other. As I've grown, well, I've realized that A) ideals founder on the human factor and B) relationships can also expand beyond three. (But it's a place to start). But I wouldn't have legally bound myself to my husband if his expectations included strict monogamy, and I think I made that clear prior to doing so.
We look very normal, very standard. But we're not.