Except it's not a threat to the future of all libraries, it's a threat to the future of "libraries" that decide to completely ignore copyright and give out an unlimited number of copies of ebooks. Basically turning themselves into book-focused piracy sites.
I'm incredibly frustrated with Internet Archive for bringing this on themselves. It is not their mandate to fight copyright, that's something better left in the hands of activist organizations like the EFF. The Internet Archive's mandate is to archive the Internet, to store and preserve knowledge. Distributing it is secondary to that goal. And picking unnecessary fights with big publishing houses like this is directly contrary to that goal, since now the Internet Archive is in danger.
It's like they're carrying around a precious baby and they decided it was a good idea to start whacking a bear with a stick. Now the bear is eating their leg and they're screaming "oh my god help me, the bear is threatening this baby!" Well yeah, but you shouldn't have brought a baby with you when you went on a bear-whacking expedition. You should have known exactly what that bear was going to do.