This week France’s lower house of parliament approved a law against inciting thinness — a classic Gallic example of good intentions spoiled by a ludicrous chain of logic. The French Senate will consider the law next.

By making it illegal to encourage someone to pursue extreme thinness, or diet to the endangerment of her health, the lawmakers suggest that they believe anorexia is a product of brainwashing — like a religious cult, the leaders of which are high fashion designers and magazine editors.

This drastically oversimplifies the causes of anorexia. In fairness, France’s legislators are not the first to do so. In the early 20th century doctors decided that anorexia was caused by a hormonal imbalance. They attempted to treat anorexics with injections of thyroid hormone, pituitary extract, insulin, and estrogen.

In the 1940s and 1950s, thanks to the triumph of psychoanalysis, anorexia was commonly believed to result from a neurotic association between fat and pregnancy, and a fear of food as an impregnating agent.

Today, the dominant trend, at least in America, is the opposite of the press-focused approach of the French legislators: It is to blame heredity. With the interest in how the role of genes shapes our personalities and determines our susceptibility to diseases, the idée fixe of eating disorder activists is that, with enough research, scientists will discover a gene for anorexia.

The focus on genetics seems as silly and simplistic as the French attempt to legislate against thinness. Anorexia involves a complex set of thought processes, behaviors, and physical consequences of those behaviors. Many of these symptoms may vary dramatically from one anorexic individual to another. To think that this phenomenon could be determined solely by a gene or set of genes defies common sense.

Anorexia results from a perfect storm of factors. Some of them may be genetic: a tendency toward anxiety or compulsiveness; an ability to endure, or even enjoy hunger. Others are environmental: messages at home or in the larger world that thinness is admirable. Others are so personal that it is hard to know how to categorize them.

Some adolescent girls diet for a while, perhaps encouraged by social pressure or press images; then they lose interest and resume a healthy, normal pattern of eating. Other girls start off on just the same course, and something quite different happens. They are impressed by the immediate effects of their behavior, how quickly the scale drops. They feel powerful, perhaps even more physically energetic. They may be gratified by the fuss their parents make over their eating and health. In whatever way, the weight loss, and their new lifestyle of self-denial satisfies a deep need to feel special and accomplished. If forced to oversimplify, I would argue that the two major contributing factors to anorexia are this intense need to feel exceptional, and the inability to satisfy it in other ways.

The French Senate should reject the law, which is both vague in whom it would target and flawed in suggesting the existence of a causal relationship between skinny models in magazines and adolescent girls becoming anorexic.

The only people for whom there is such a direct relationship is the models themselves. If you are paid to be extremely thin, then, yes, in a sense you are being “incited” to thinness.

The 2006 death of the Brazilian supermodel Ana Carolina Reston from anorexia suggests that the fashion industry, and particularly agents and managers, should be policed more than it currently is.

Spain’s decision two years ago to ban models from the catwalks who had an extremely low body mass index hardly caused a change in the industry, but it was at least targeted to protect the right people. One would hope Reston’s death would provoke a serious discussion about the risks of modeling, and that editors would shy from using emaciated models in their pages — for the sake of the models themselves.

Ms. Taylor is the editor of an anthology, “Going Hungry: Writers on Desire, Self-Denial, and Overcoming Anorexia,” which will be out in September.