The rhetoric of disgust is common in moral discourse and political propaganda. Some believe it's pernicious, for it convinces without evidence. But scientific research now suggests that disgust is typically an effect, not a cause, of moral judgment. At best the emotion on its own only sometimes slightly amplifies a moral belief one already has. Appeals to disgust are thus dialectically unhelpful in discourse that seeks to convince. When opponents of abortion use repulsive images to make their case, they convince few, even if they rally their base. When champions of animal rights show graphic depictions of the torturous conditions of animals in factory farms, they convince only those previously ignorant of the severity of such conditions. Ultimately, disgust may be less pernicious than it is useless.