Publishing a book is selling your work to someone who effectively uses a shitty photocopier to sell lots of copies to lots of consumers (I'm aware that publishers can, in an ideal world, provide access to quality editors whose involvement improves the work, but I think my point still stands). Or, in a minority of cases, releasing work for free.

But in both cases, the writer is actively inviting people to consume what they have made. Those people will plagiarise to a greater or lesser extent on a large spectrum from drawing personal inspiration on a subconscious level to AI powered supercharged fraud.

I believe the grandparent comment is saying that an expectation of privacy and freedom from plagiarism is incompatible with the act of publishing, be it through traditional third parties (publishing houses) or modern ones (social media).

I would tend to agree. Publishing is primarily a commercial action.