I think the biggest trouble with explaining proshipping is that most everyone IN THEORY is 100% pro-archival and literacy, but IN EXECUTION, each person has a unique "of course THIS is the exception" breaking point that they see others as reprehensible for NOT also having.
Like, here are some VERY COMMON examples of personal breaking points that can come up in archiving:
Trans person whose friend keeps writing Harry Potter fanfic
Parent whose coworker loves drawing shota/lolicon
Uncle going down an anti-vax documentary hole
Mom pushing diet magazines on her daughter
Racist old dudes on school reading lists
True crime Youtube clickbaits
AI-generated Elsagate brainrot shorts
Comic books by a white guy posing as Asian
$2 exploitation porn DVDs
School shooter simulator video game
Guides on making explosives
Odds are pretty good that at least one of those made you, reading this, viscerally cringe and want to argue about, WHICH IS WHAT I MEAN. Every person has a breaking point, and THAT'S NORMAL.
The point of the library training isn't to make you into a unique person who has never, ever been reviled by or wanted to destroy a piece of media. It's to learn how to live with that feeling, step back, and work with your team to maintain the archive, anyway.
And sometimes, maintaining means recognizing that not every place IS an archive! I'm only able to maintain an archive space BECAUSE I know I have spaces where the stuff that revolts me is banned! It's okay to curate multiple spaces; tolerance is more than blind acceptance.
The library archives information, the bar should not be allowed to become a Nazi bar. The AO3 tags archive every fic, the Discord group chat isn't made to be a museum. You don't have to take everything home with you at all times to prove yourself.
All you really should do... is support your local libraries with a card and some check-outs! We have movies and audio books and video games and printers now! It's cool!