You are vastly mistaken. My wife and I are lifestylers (swingers) and our marriage is a thousand times stronger than it ever could have been. I think you don't understand it because you have never done it. It's like explaining what ice cream tastes like to someone who has never had it.
From experience, I can say that it does not create a disconnect from the primary relationship as you stated. For us, it caused a fortification around our relationship, opened lines of communication, allowed unfulfilled fantasies to become reality, caused life long friendships to develop over years and created trust in an area (sexual fidelity) riddled with distrust in today's marriages.
Many many years ago, my wife and I were the typical traditional marriage. I loved my wife, but I was becoming more and more uninterested in her physically because we were in the same old routine, day in and day out. Our marriage was dying because there was no passion, adventure or excitement. We tried to "manufacture" excitement (vacations, going to new places, games, etc...) but the problem was that we were suppressing all of our sexual fantasies - both of us. One day, my wife opened up to me about one of her fantasies and it literally transformed our marriage. Within a month from that day we had fulfilled her fantasy, and we went from grudgingly having sex 1-3 times per month, to a passionate 4-9 times per week (with each other), and 1-3 times per month with other couples.
Our most "happily married" friends are lifestylers (swingers) and our most "problematic marriage" friends are vanilla (straight), and we know hundreds of couples in both arenas.
We say: "It works better than traditional marriage! and just like traditional marriage, it is not for everyone and just like any human endeavor, it can fail."
The O'Neill's were at the forefront of "swinging" as you stated, and just like version 1.0 of the computer (remember the Commodore 64?), a LOT has changed since then (read: The Internet).
Dear Brett, monogamist relationships dont work at all (80% of Serial Monogamist) they are all SERIAL MONOGAMIST Sex is something between two adults and is highly individual....
We are very happy and love each other very, very much! We started to play (we are softswingers, everything is Ok except intercourse) with other couples and single girls (i proposed to play with a single guy but she says she can handle this) about one year ago. We had a lot of experiences and I enjoyed it a lot. From my point of view, my wife is enjoying most of the time during the experience (she is very active with everybody and we have fun for couple of hours), but the next day she is expressing remorse, shame, disgust and she feels like she did something wrong....
I love my wife very, very much and i love the live with here and all my sexual phantasies are always including her! She is 32 years old i am 42 years old. Sometimes i think it is to much for here...
I am enjoying almost all experiences and happenings as inspiring, fun, creative and full of live. It touches me deep inside and feel super confortable, alive in this situations. I feel like i share everything with my wife and i always feel close and intimate with here. Actually i have the feeling it brings us extremely close..
My biggest fear is to end up like most (actually all of them) of our monogamist couple friends = divorced, cheating or they are in a brother / sister relationship.