I think there are two issues here:

1. If someone is acquiring books in bulk for bargain-bin prices and shredding them, they're books whose physical copies have essentially no market value and which, absent this buyer, were overwhelmingly headed for pulping or landfill anyway. Millions of books are destroyed every day.

Could one of these worthless looking books turn out to contain information historians care about in a 100 year? Sure. But that doesn't create an obligation for someone to pay to warehouse every extant copy forever. Physical Preservation has costs: space, cataloguing, handling, transportation etc. Archives and libraries have always had to make choices for this reason.

2. I'm not arguing that preservation has no value. The question is whether destroying a physical copy after digitizing it is a serious loss when talking about mass-produced printed material.

Was this the last surviving copy ? Is the information unavavilable in libraries, archives, other editions, scans, citations, contemporary works etc ? If not, nothing has been lost except one physical instance of a reproducible object.

Your film analogy worked a lot better because old film footage is often unique primary source material. A camera recording of a random brooklyn street in 1993 may literally be the only recording of those people, storefronts and circumstances. The nth printe dcopy of a technical manual is not analogous to that.