This is exactly my worry.
Suppose that on some level, this was possible. You wouldn’t see nice, cozy instances of people who’ve finished their old collection selling them to low-income folks that just got their first Steam Deck. You’d put some games on sale for $10, and an automated Python script would automatically buy them and put them back up for sale for $49.98, one cent less than the new copies being sold.
When literally every single digital copy of a game is “equivalent”, the used games market just doesn’t make sense - although there’s a hundred third-party sites that would like it to work that way so they can take their un-earned cut.
I could in some ways understand their pursuit of emulators when they’re monetizing those same games currently (even if I disagree with their pricing structure on them). What really got my goat was when they went after Garry’s Mod animations, a medium that has promoted their visibility and never conflicted with their software sales in the slightest.