Once metadata gets incorporated into a Nakamoto blockchain, it enjoys all the benefits of the peer-to-peer network that curates it. The entries are accessible to anyone on earth who has a computer and an Internet connection. In order to destroy them, you would have to access every computer on the network (and someday, perhaps, even a constellation of satellites). They are impossible to change, and thus impossible to censor. And they carry with them both a time stamp and cryptographic proof of who created them.