Everybody has different views of the world. shrevecouple, I'm with you. My wife and I look for swing partners, not love partners. But, plenty of other couples are looking for more emotional grounding in the sex partners they play with. If it works for them, great. It can be difficult, but so is swinging itself.
All you can do as a friend is to voice your concerns (which you have) and let them live their lives as they will (which you have).