On its own that seems like a pretty weak justification, at that point we would need to preserve every copy of every book forever because you never know what what useful physical material it has on it even beyond its text. That extends to non-book items as well, and while I understand the idea it's just not realistic in any sense.
I think the more important part is to define what "rare" actually means and save/digitize set copies of those books that are actually at risk of being lost completely (rather than letting them rot away somewhere or get bought up to be privately destroyed). I suspect many of them are just not at all interesting enough to justify the expensive though.
I think the more important part is to define what "rare" actually means and save/digitize set copies of those books that are actually at risk of being lost completely (rather than letting them rot away somewhere or get bought up to be privately destroyed). I suspect many of them are just not at all interesting enough to justify the expensive though.