I think it depends on who you are as an individual. I don't buy the whole "humans are a polyamorous species and monogamy is unnatural and restrictive " anymore then I believe it to be the other way around. I think Humans are a very complicated species, and as a result so is our sexuality. I dabbled with polyamory years back with someone I had been head over fucking heels inlove with who was polyamorous, and he had convinced me to try it with him. I had always been in closed relationships prior to that, but it was after a huge break up with an ex, and I was going through a "fuck the world and everything else" phase. People say polyamory is suppose to make your relationship with those you're involved with stronger then those in a monogamous relationship. In the beginning, I tried convincing myself that this was the way to go and that I'd never be alone or sexually frustrated again, but after a while I found what I actually knew all along, and that's that for me adding more lovers to the mix only diluted the bond rather then making it stronger, and after a while I just started looking at these people more as my friends then my lovers. More of a FWB sort of deal. It wasn't a negative experience, but it was nowhere near as satisfying or as strong as the monogamous relationships I had been in over the years. I'm married now to someone who also experimented with polyamory, and came to the same conclusion long before we met. The need to be close to other people sexually isn't there for either of us. Could our marriage eventually fail? I very highly doubt it, but anything is possible . However if for some reason it ever does, I can say with total confidence it will have nothing to do with falling in love with someone else. People can argue that all they want, but the fact is I know who I am, and even with all the changes I may go through as an individual, the fact still remains that I simply don't work that way.
However, I am very good friends with lots of people who have been involved in polyamory for years and who are very happy with it and their relationships. And that's wonderful! Everyone should feel secure and happy with what works best for them!
If you're curious about it and are wanting to see if it's your calling, by all means try it and see how you feel. If you like it, more power to ya, and if you don't, that's equally just as right and beautiful.