You don't need consent to modify an artwork. When you put your art out for people to consume your consenting to the viewing, and saving it for their use.
Like modifying a game console/ radio you bought from the store.

And the people who say that "its lifeless" is emotional speaking. It comes from people but not from the person putting in a prompt.

The main issue is people plagiarizing other artists work as their own and profiting from work thats not theirs.