There are laws about copyright and trade secret.
> They haven't lost anything - just took a copy.....
Correct. This is why it's a copyright violation and not a theft.
> [...] fair use....
Fair use is also a legal term, and it has some (reasonably) specific meanings. It's noteworthy that the large copyright protection industries don't respect those terms and have automated DMCA takedowns to abuse people for things which age legal:
"the fair use of a copyrighted work, including such use by reproduction in copies or phonorecords or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright."