@Snowmama
The part about the guy in a MMF threesome not wanting his GF to have vaginal intercourse wasn't about Dan Savage himself (he's gay). It was about one of his readers.
Savage's stance on GGG isn't that you should do whatever your partner wants and be up for it, regardless of your own views. He does think that you should be able to TRY most things a couple of times, but if you REALLY don't like it, your partner should respect your wishes. And if you're not crazy about it, but it's just 'ok', but your partner really enjoys it, you should do it every now and then. Something which I wholeheartedly agree with.
I've been reading his column and been listening to his podcast (which is even better imo) for a couple of years now and tbh it's really changed my sex life. Before I was always afraid to divulge my fantasies etc, afraid of what people might think and WAY too eager to please. In my last few relationships there has been a ton more honesty and openness, much, much better sex, and mutual respect.
But to get back on the topic of nonmonogamy, I think he often forgets to realise that if one partner asks to be allowed to step outside the relationship, it can be very hurtful to the other person. I agree that it's probably still preferable to cheat outright (and for the record, he doesn't think that going behind someone's back and having an affair is a commendable thing), but I agree that there will probably be something of a power shift. Still, I'd rather have my partner voicing these issues to me than just outright having sex with someone else.
Another thing on which I do agree with him, which I don't think has been mentioned in the article, is that affairs sometimes do save a marriage. I remember one example in his podcast I think, where the husband had become severely disabled and sex was out of the question. The wife took care of him for the rest of his life, but had a (very discreet) affair on the side... Really, is that such a horrible thing? As he said, it stopped her from going insane, and kept the family together in a way.
These things are worth thinking about at least. After all this time I'm still not sure if I could ever handle it myself, my partner wanting to have sex with someone else (without me). But there are so many things in between, I've had a couple of threesomes within my current relationship (which just happened, really), and it actually brought us much closer together and just affirmed to me that we have a very strong relationship indeed. Maybe it would work in the same way, maybe not. For now we're very happy with just each other, but 20 years down the road? Who knows where we'll be in our relationship then, and I truly believe that if you try to keep talking honestly to each other that will solve a lot of problems before they even begin...
(Ok, such a rambly post, and sorry for mistakes, English is not my first language!)