To “publish” in the web is a delusion. A blog is about as public as a widespread porno magazine subscription. Everybody can read the content at home, on the writing desk, but there is no collective testimony whatsoever. When we speak of the public in reference to the internet we confuse public with accessible. Public refers to a collective testimony, not to systems of media storage and individual display.
The words that appear and disappear on the screen aren’t public in the same way as we have gotten used to this term since the idea of the public appeared in the middle of the 18th century. If somebody speaks in public, that person stands with his or her integrity and with the reliability of any natural person for what she or he utters.
But most of all it is the mixture of privacy, publicity and publishing taking place in apps and other tools that display the web’s content, that causes the non-public character of the internet. A computer most of the time is a private tool as well as a professional one, but not a public tool.
Being a private tool, which you can use or not, it doesn’t define what is public and what is not.