Just another angle on this, from a Mumsnet perspective though.
It does frustrate me when women post on here about having affairs and they do the "re-writing history" bit. As justification for what they are doing, they claim that they knew before they were even married that the relationship wasn't right, or that there was no chemistry, which does beg the question - well, why have you waited to have an affair to exit a relationship you always knew wasn't right?
Or could it be that in fact your relationship was never this bad, but you need to believe that it was, to justify what you're doing now?
In those cases, I think it's fair enough for respondents to query why women went ahead and married men they didn't love. If someone is deluding themselves that they have in fact been a victim, when until OM came along, they would have thought no such thing, it can be helpful to have that delusion challenged.
I also dislike the practice of only having the courage to leave a relationship when an alternative beckons. Often, people would be better served by striking out on their own and reviewing a past relationship in an objective light. People tend not to be objective about the relationship they've left when they are already involved with someone new and shiny. I think this is why so many of these "new" relationships fail - once out of the "love haze", the previous relationship (and person) doesn't seem so bad after all, there is a belated realisation that had it not been for the affair, the relationship could have been successful.
I have far more respect for people (men and women) who realise that they made a mistake marrying, take responsibility for that decision and end the relationship. I've also got a lot of respect for people who have the courage to live on their own and stand on their own two feet, instead of expecting someone to "take care of them".