FWIW, it is not clear to me that "receiving $50,000 if the other spouse sleeps around" is actually one of "the rights marriage traditionally gave them", so I think the essayist is stretching the truth there.

It's certainly not a specific right ever guaranteed by the institution of marriage, but there used to be some rather strong legal hammers wielded against adultery (especially against that which was committed by women,) and some couples would like to have some comparable hammer on hand for their own relationships.