There’s the obvious harm that some people are just not equipped to see these graphic images, especially with no warning. Like people who have trauma from being in or around the acts being depicted
You might enjoy this, by a colleague of mine. It's a rarer situation, but this could be one harm pathway for those types of images. (In most cases, exposure is a good thing for people with PTSD)
https://journals.sagepub.com/doi/10.1177/2167702620917459
Perhaps those people can refrain from jailbreaking ChatGPT to produce graphic imagery. There is not a single person in the world who will type any of the prompts noted in the article by accident.
https://journals.sagepub.com/doi/10.1177/2167702620921341
(Research aside, it seems unlikely to me that a lot of people would stumble on that prompt accidentally in any case)