What are non-Muslims really doing when they refrain from drawing Muhammad?

Jeet Heer writes in TNR:

Art Spiegelman’s comic strip commentary on the Charlie Hebdo controversy, “Notes from a First Amendment Fundamentalist,” delves deeply into these issues. In the cartoon, Spiegelman (limning himself in his stylized rodent form, developed for his graphic novel Maus) is holding two magazine covers (images within an image). One, titled "No Problem," features a standard smiley face and says, “Have a nice day.” The other, titled "Problem!," features the same smiley face wearing a turban and identified as “Mohammad.” As the contrasting images show, it takes just a few squiggles and a label to turn a smiley face into a blasphemous provocation. The offense isn’t so much in the image as in the intent. To say you are drawing the Prophet is the scandal, more than what is drawn. A drawing of Muhammad is an idea or an assertion more than it is a physical thing. . . .

Adherence to a rule that Muhammad should not be depicted is a very curious thing. Abiding by the prohibition can’t be an act of belief, since these publications aren’t run by Muslims who believe the prohibition is crucial to their faith (and in any case these publications have a secular mission and identity). Nor can the prohibition be just about displaying sensitivity to Muslim sensibilities since there is no consensus among Muslims that the prohibition should be adhered to or is binding among non-believers. In fact, certain strands of Islam, notably those in Iran, have a rich history of depicting the Prophet. A thorough prohibition on depicting Muhammad would, if followed by all, mean the banning of a rich vein of Islamic art.