That's not what she's saying though is it?
She's saying, as an adult, who presumably has entered into some sort of commitment with his wife, it's not her job to make sure he sticks to it.
This is what I don't get on all the "shall I email the trollopy tart who has pinched my husband" threads. No,you should pack your husband's bags. The other woman is irrelevant.
I'm another one not remotely jealous. I spend 3 mths a year away from dp, and haven't a clue what he gets up to while I'm gone. I have friends who think I'm insane for "allowing" him out at w/es with his mates, but I see that more as a sign of their own insecurity than of the fact that my dp is shagging every woman in town.
I wouldn't want an open relationship, I'd actually be quite happy never to have sex again as long as I live I think, but that said, I don't really see (apart from it being a huge insecurity thing for some) why anybody would find open relationships between consenting adults so scary.
Biologically, as has been said, an open relationship is far more natural than the concept of "romantic love" which was a literary device invented by 19th century writers. (not that open relationship gives someone free reign just to fuck over (metaphorically) anyone they feel like doing of course.
It would also be interesting to see how many of these spurious people (because presumably some women lie too) say they aren't married when/if asked the question.