You're conflating the archival properties of the medium with the decision about what to save. Oil paint on canvas is durable. It doesn't mean that a museum needs to retain every piece of crap that anyone paints.
The problem is that removal of content because it's crap/immoral versus operator destruction is not a meaningful distinction, from a software perspective.
So it would probably need to be write-only to prevent people from burning it down, which would necessarily mean that, once content is included, it cannot be modified or removed.
So it would probably need to be write-only to prevent people from burning it down, which would necessarily mean that, once content is included, it cannot be modified or removed.