IT’S been another big month for talking about women’s bodies.

Just as the White House hosted the first United States of Women summit meeting, which culminated in Oprah Winfrey’s noting, in conversation with Michelle Obama, “We live in a world where you are constantly being bombarded by images,” across the ocean the new mayor of London was announcing a policy that would ban ads on public transport that might cause women to feel pressured “into unrealistic expectations surrounding their bodies.”

Mayor Sadiq Khan’s policy sounds, on the surface, like a big step forward. Down with fat-shaming! But it is, rather, an old idea, and one that reinforces stereotypes instead of grappling with the real issue: How do we change the paradigm altogether?

The immediate impetus for the ban, which will be carried out by the London transit authority via a steering committee that will rule on ads case by case, was a 2015 diet pill ad depicting a very tan, very curvy woman (the kind who is a staple of lad mags) in a bright yellow bikini alongside the words, “Are you beach body ready?” The implication was that if you had not achieved the unrealistic proportions of a Barbie, you were not. The public protested (a petition on change.org received more than 70,000 signatures), and Mr. Khan made it part of his election campaign.

The regulation follows decisions by the Advertising Standards Authority of Britain to ban certain ads, such as a Gucci shot that depicted what was deemed an “unhealthily thin” young woman. Though often conflated with the movement to protect models, which resulted in legislation in France in 2015 requiring models to produce a doctor’s note attesting to their health, and digital alteration of photographs to be disclosed, banning is a separate issue. It doesn’t involve working conditions (which can and should be legislated), but subjective, and ultimately regressive, assumptions about what constitutes a positive female image.