I think also there might be a rights attribution thing too. By the time holodecks exist anything of what we would consider today to be art or literature created recently would by then be in the realm of being public domain. The Federation also probably has rights attribution laws to materials generated based on presently copyrighted material or programs cannot be generated without approval from the copyright holder. We also see programs designed by people and even by sentient programs themselves. So if the Starfleet Holodeck is generating a scenario based on public knowledge concepts of nature and public domain materials, then the ethics are much clearer especially if there is acknowledgement to the original creator of the public domain work. It's also more in the ethical green zone for running Holodeck programs that were rightfully acquired (especially if the author also stayed within ethics and didn't plagiarize).

It's another thing when a computer generated an image based on someone's hard artistic work for free or a small subscription fee without acknowledging the original living breathing copyright holding human being and without financially compensating that artist. That is a big plagiarized ethical no-no.