The technique of obscuring the difference between legislation and custom is well entrenched in talmudic and post-talmudic rabbinic literature, especially that of Ashkenaz (Europe); neither Zimmerman nor Knohl invented it. However, the needs of men and women informed by the values of our society are very different from those of the unlearned Ashkenazi masses of the past. The use of this technique in contemporary handbooks encourages the type of conformity typical of unlearned societies, rather than the diversity that comes from individuals making informed decisions.
Moshe Benovitz, “A Lifetime Companion to the Laws of Jewish Family Life and Man and Woman: Guidance for Newlyweds (review),” Nashim: A Journal of Jewish Women’s Studies & Gender Issues vol. 12, no. 1 (2006), 319.