- Porn is done under consent, where participants should be reasonably aware that it will be published
- Porn tarnishes reputations
If you pasted Daisy Ridley's face in a crowd in, say, China, doing every day stuff, no one would rightly care because there's no real potential unless you are doing it for some ulterior motive.
They have been, since inception, illegal, in the sense that they represent a tortious act. They might be illegal in the criminal sense, depending on the jurisdiction, even in the US if absent meaningful context bringing the fake under the protection of the First Amendment as a form of speech.
What if I make a fake video of a specific person being physically attacked?
He didn't consent to be attacked and it may tarnish his reputation. Is it unethical to do any of the above?