I think I prefer the legal definition of theft. Theft is unlawful removal and deprivation. I can steal ideas all day long from Mark Twain or Shakespeare and they remain exactly the same.
Writers don’t steal from others. Copy or paraphrase or embellish, sure. There’s always been a fine line between using someone else’s ideas under your own name, and drawing on cultural resources.
It’s not as if Mark Twain or Shakespeare thought up all their own material.
And neither does any other writer. The very nature of information encoded outside bodily resources means that we depend on cultural continuity for our lofty position in the animal kingdom.
Ideas, information, understanding. All of it must be retranslated for new generations, new languages, new audiences.
This is not to say that our continued progress in understanding and knowledge of new realms of science or new places across the cosmos leaves us unable to come up with something new from time to time. Even as a child, the idea that everybody would carry a supercomputer in their pocket that could broadcast to a global audience was a wild fiction. Now, it is something that has rendered much of our un-wild fiction hopelessly obsolete.