here's the thing about swinging: if people had no emotions, it would be good old dirty fun. because we DO have emotions, it's a poor idea, statistically, in a committed relationship. think about this: if your significant other suggests it and you're NOT into it, he can tell himself, "man, she's no fun; she's limiting our relationship; we're not seeing eye-to-eye; she's closed-minded." if you DO agree enthusiastically, and if you enjoy it, what do you think is going to run through his mind? "wow--maybe she's been looking for a reason to sleep with other men."
suggesting something like that is a subconscious test of either OBEDIENCE (will she go for it if i suggest it?) or of LOYALTY (will she refuse, and can i therefore justify cheating myself? i mean, hell, i offered her the opportunity to join me. her loss.). and a man who uses a test that can't be satisfactorily passed is an insecure jerk. it's an excuse to either cheat on you because you're not enough for him (if you don't go for it) or to respect you a little less (if you go for it).
look, in the context of a NON-longterm committed relationship, like a "buddies" scenario, it may work well, it may be fun. but if you LOVE someone, it makes you sad and sick inside to think of them sharing something so intimate with someone else. if you don't want to do it, DON'T FRICKIN DO IT.