I agree, as long as there is communication, honesty and both people are clear on what they're looking for then it can work. Oddly enough, with all that openness and communication that purely sexual relationship has to grow a certain level of emotional attachment. I think that jealousy from one person or another is the part that dooms it. So, with that said, why not just having a functional (emotional) relationship with a lot of sex? Good times all around and nobody goes home jealous.