Here is my take on this:
Differant strokes for differant folkes. Not every couple shares the same ideas of intimacy as everyone else. Some couples feel that adding another person to their sexual experience enhances the love they feel for each other. Allot of guys get off watching another man pleasure their woman. Many women get off watching another female get their back blown out by their man. I personally would not ever want another guy touching my women but to each his own. Just because the "standard" marriage means no sexual contact with anyone besides your spouse does not mean that every marriage is that way. I think couples that trust each other enough to enjoy exciting sex are better off than the couples who cheat on each other. I enjoy the double standard and so do allot of woman as well. Many women these days are curious about other girls and why not? Women are beautiful. So...if your women has no interest in other men(which is how you would ideally want it-being a man anyway) and she understands that if you were to be with another women(and her) that it is only for fun, why is it so bad? Granted you really have to be secure in your relationship or problems can arise. It depends upon your maturity level when dealing with sexual issues. I think the sex itself is differant when another person is added. When you are with your lover you are more intimate and when you are in a 3some it has a differant dynamic. It isn't "making love" so much as well...hot fucking. It turns couples on later when they are just with each other thinking about the hot time they had.
There are definately problems that can occur when you mess around with this stuff, so you guys are right about that. Someone could get jelous or maybe you might really like the girl you have the 3some with and she might want to screw you without your partner etc...lots of things could happen. That is why I think you need to think it out properly and find the right person to do it with. I really think it is best with someone neither of you will see again or at least someone who would not turn into anything more than just sex. I guess that is why swinger couples pick people up at bars and such(way to risky if you ask me).
Look at it like this: if you marry or are with someone that is what you consider to be your "soul mate" and she is incredibly intelligent,beautiful,funny and whatever other wonderful traits you desire- then when you together seek another female to throw in the mix, it is more like she is a toy for you two. See what I mean? I have some younger friends(19-21,I am 29 my girl is 23-so you dont think I am an old creepy swinger or something) that I have known for a long time and when they have house parties there are always some young hotties there that like to get busy. They are the best because we are only attracted to them physically(they are usually not the smartest or most intellectually stimulation creatures) and that way it is just fun. Cute,young,not so smart,hot- you get the picture. Like hot little fuck toys- that sounds bad but that is how allot of guys look at ALL women. I think those that are into this might understand what I mean. Basically just fun girls- no one you would really want to date or whatever. Girls like that are great, they are a blast to hang with and it creates a wonderful sexual tension.
In general I am against "swinging" because that denotes that you are into MMF which I am NOT into. I just think you should keep an open mind because you only live once and you dont want to die with regrets. I dont ever want to be that married guy(I am not married now) that pines away for his secretary or some shit like that. I dont believe in cheating, in fact I have no problems being completely monogomous. I do however think that if you do have a female that is into girls you might as well take advantage of it from time to time.
Lets hear from some of you that have actually done this with your lover and are still together. I wonder what the statistics are on marriages staying together when 3some's are part of their relationship. What do you think? Would you think it would hurt or strengthen the relationship?