The absence of possessiveness and jealousy. I can admire those qualities...
Oh, there are rules. You have ok it with your partner, have to have permission, give consent.
Furthermore, the reasoning for it, is that it's not cheating if the other person knows.
Also, many of the couples have issues within the relationship, and bringing other people is supposed to alleviate those issues. It does not, they still exist.
The men are not possessive because, well, many have an inferiority complex. Liking to see another man hitting off their significant other has a whiff of "beta" to it. And then encouraging said men to "get her done"?
Well, the women get theirs. But ask yourself, what type of man is that?