This argument is even more ridiculous than it seems. During the copyright office hearing for this exemption request (back in April), the people arguing in favor of libraries talked about the measures they have in place. They don't just let people download a ROM to use in any emulator they please. It's not even one of those browser-based emulators where you can pull the ROM data out of your browser cache if you know how. It's a video stream of an emulator running on a server managed by the library, with plenty enough latency to make it very clearly a worse gaming experience.

It's far easier to find ROMs of these games elsewhere than it is to contact a librarian and ask for access to a protected collection, so there'd be no reason to redistribute the files even if they were offered, which they aren't.

On top of that, this exemption request was explicitly limited to old games that have been long unavailable on the market in any form, which seems like an insane limitation to put on libraries, places that have always held collections of books both new and old.

All of that is still not enough to sate the US Copyright Office, the ESA, AACS, or DVD CSS. Those three were the organizations that fought against this.