Actually, the act of copying a work covered by copyright is not itself illegal.

I'm going to need you to back that up with a source. Specifically, legislation.

If I check out a book from a library and copy a passage (or the whole book!) for rereading myself or some other use that is limited strictly to myself, that's actually legal.

What you're getting at here is the fair use exemption for education or research, which I have already explained. When considering fair use, it has to be for specific use cases (education, research, news, criticism, or comment). Then, after that, the first thing the court considers is whether the use is commercial in nature. The second is the amount of copying.

You checking a book out of a library and copying down a passage will almost certainly be education/research, and probably noncommercial, so it will most likely be fair use. Copying the whole book might also be fair use, but it is less likely to be so. Copying a book for a commercial report is far less likely.

The fact that it's "strictly limited to yourself" has no real bearing in law. Like I say, this isn't research - they're not writing academic papers and releasing their dataset for others to reproduce and prove their work - and even the earliest versions of their training have some presence in the existing commercial product they have developed. Their use is thus not research, so not fair use, and even if you considered it as research it is highly commercial in nature and they are copying full work into their training dataset.

Bringing in the whole "the law treats corporations as people" is further proving you don't really know how IP law works. Just because something is published and freely accessible does not give the reader unlimited copyright to it. Fair use is an extremely limited exemption.