It seems to be undermined by the same principle that says that going into a library and reading a book there is not stealing when you walk out with the knowledge from the book.

OpenAI seems to feel that way about the their use of copyrighted material: since they didn't literally make a copy of the source material, it's totally fair game. It seems like this is the same argument that protects DeepSeek if indeed they did this. And why not, reading a lot of books from the library is a way to get smarter, and ostensibly the point of libraries