However my own opinion is that all of the lists may be subscribed
to by anyone. Many do. Many archive sites subscribe to the mailing
lists and archive the messages. Full archives of all of the
messages are therefore easily available elsewhere. The archive is
not of subscribers. The archive is only of messages from people
who have posted to them. Anyone who posts messages to public
mailing lists must expect that the public will read those messages!
Indeed, and _anyone_ can subscribe to a list and our (the GNU
projects) policy has also been not to require users to subscribe to
lists to be able to post a bug report, or a question (though things
might go through a moderation queue).
Most of the lists also go trough a NNTP <-> SMTP gateway (like GMANE).
Not providing the archives is a disservice to fellow hackers. Having
list archives available easily it makes it trivial to import a mailing
list and browse through the old traffic for previous bug reports,
questions, and what not.