For some scenarios, it's not the image itself but the associations that the model might possibly make from being fed a diet of 4chan and Stormfront's unofficial YouTube channel. The worry is over horrible racist shit, like if you ask it for a picture of a black person, and it outputs a picture of a gorilla. Or if you ask it for a picture of a bad driver, and it only manages to output pictures of Asian women. I'm sure you can think up other horrible stereotypes that would result in a PR disaster.