i'm pro open relationships because i don't think any one person is ever going to be everything any one other person needs. i, and most of the women i've ended up with, have had needs we couldn't meet for each other, or desires for sex outside of the primary relationship. with ones where we agreed on monogamy, this tore us apart. i'm much happier now in a relationship where we don't do much outside, but have the freedom, and have that acknowledgement of our needs and desires.
i'm also just honest with myself that having one primary partner for the rest of my life would be okay with me, but only being able to fuck one person for the rest of my life would drive me batty. i'm a slut*, whatever.
it's not necessarily easy, my lady friend and i have had to have a lot of serious conversations about our feelings, boundaries, what we need from one another, and no open relationship can survive without that, but that's another plus, in a way. in a lot of monogamous relationships, these things are simply assumed and never discussed, and that hurts the relationship.
it can also be hard to break down your own jealousy and insecurity, but those things are bad no matter how you look at them, so it's worth working on them, and to be willing to slow down and take baby steps with things if that's what your partner needs.
it's hard to have a perfect relationship, and that's not going to be dependent on whether it's open or closed, but on how you conduct yourself in it. like i said, i don't think any one person can be everything to another, but a lot of people still survive in monogamous relationships. i do think, though, that openness forces a lot of the practices that any good relationship needs, and it has the added bonus of being able to follow your desires and meet your needs.
open relationships are where it's at, imo, and maybe everyone doesn't want it, but i do think many people would benefit from trying it or at least learning from that relationship model.
*and i mean "slut" in the most pro-slut, sex-positive way.