This isn't the defense you think it is. Performing a copyrighted work from memory - e.g. a piece of music, a poem, a story, etc - is still a copyright violation. There's no special protection for works that a human has memorized.
Humans are not judged on the basis of what they _can_ do.
Reasoning about how to constrain tools on the basis of what they _could_ do, if e.g. used outside their established guardrails, needs to be very nuanced.
Who's liable for the copyright infringement if you can coax it out of a system? If you can bypass paywalls by using google's cache feature (or since they got rid of it, but using carefully crafted queries to extract the entire text via snippets), is google on the hook or the person doing it?
Is it? There's plenty of people prosecuted for running illegal streaming sites and torrenting (which involves uploading), but I don't know of any efforts to crack down on non-distributors.
2. Google might not be the most sympathetic defendant, but what about libraries? They offer books to be borrowed, and some offer photocopiers. If you put the two together, you get a copyright infringement operation, all enabled by the library. Should libraries be on the hook too?
that is quite different. Google serves (used to serve) to its users whatever the website presents to its crawler, it does not try to avoid paywalls or interact with the website in any capacity other than requesting information