That won't fly because it is just as easy to lay claim that ignoring copyright is against the public because it devalues private property rights of which the creator did not assign to the IA.
But there are things in that response to distinguish IA actions and motives from other bête noires of Copyright law (The Pirate Bay, etc.) That would give IA and their supporters something to work with; intents, outcomes, and the limited nature of IA NEL would (hopefully) harness publishers opportunism in the view of the law.
[1]: https://www.copyright.gov/laws/hearings/Sen-Udall-Response-N...
And it was a gesture that was not theirs to make. Did they ever consider just asking the publishers for permission? They might actually have gotten it. Companies were quite eager to do things to show they were trying to help back in March and April. But I've looked and found nothing saying they asked, so I'm guessing they didn't. Probably because they thought asking would look bad if they were told "no" and did it anyway.
We are a society of laws passed by representatives, not formed in one's mind on the spot.