I’m wondering if perhaps the problems Jothar’s Rav associated with workplace/joint vacations or meals issues are not that “untznius things” happened as a result of same, but that overly familiar interaction leads to meandering thoughts and shades of disappointment in one who was previously enamored with his wife. That can be a shalom bayis killer, however subtle and slowly.
Perhaps this is EXACTLY why the divorce rate amongst the general populace is so rampant. Perhaps there is a world of difference between politeness in the workplace (thank you, Mrs. SoandSo), nodding good morning to the Mrs. Neighbor, and laughing/joking, sharing a light moment, first name basis with female colleagues, joint vacations/meals that promote shared light moments and shared laughter/fun.
The general populace, who has an abundance of experience interacting with opposite genders, seem to have quite a challenge in the “staying married” department.
I know that some couples are able to have joint meals in which the men are able to greet courteously (not over familiarly) and thank sincerely for the food, inserting specific comments of thanks, and not engage in light conversation between genders. The enjoyment of the shared meal is for the two wives to enjoy each others company and the two husbands to enjoy each others company. I don’t know Jothar’s Rav, but I don’t think that in general, the above scenario is what Rabbanim are concerned about.