I disagree that there are people who are totally mono. After all, everyone feels some level of love for friends or even acquaintances who endear themselves in one way or other. I think people figure out ways to draw boundaries that allow them to separate monogamous love from other kinds of love. It is taboo to consider feeling sexually attracted to friends or strangers and so people must tell themselves that when they're seeing attractive people on TV, the attraction isn't physical (they probably just don't think about it consciously at all).
Anyway, I don't think anyone is totally mono-amorous but I also don't think it's any less natural to control how you express you love than it is to control what and how much you eat. The problem, imo, is that people have gotten side-tracked from thinking about what is healthy and ethical in terms of relationships by strict, shame/fear-driven ideologies about how they have to live in order to be socially accepted. Obviously there is tension in everyone on this subject or it wouldn't be so taboo to even consider talking about polyamorous feelings with friends, family, etc.