Lee Siegel writes in the New York Times Sunday Revies:
The problem is that the cartoon accurately portrays a ridiculous real-life caricature that exists as literal fact in the minds of some people, and it portrays it in terms that are absolutely true to that caricature.
An analogous instance would have been a cartoon without commentary appearing in a liberal Northern newspaper in the 1920s — a time when Southern violence against blacks was unabated — that showed a black man raping a white woman while eating a watermelon.
The effect of accurately reproducing such a ridiculous image that dwelled unridiculously in the minds of some people would have been merely to broaden its vicious reach. The adherents of that image would have gone unsatirized and untouched.