In the rare instance where I've felt inclined to send to all of the people CCd in an original blatherbit, I have always made it a point to append the comment that:

"Your email address was provided to me, and possibly to every spammer on the network, by the message I received from your friend <<<name of sender>>>. Please suggest to your friend that basic email courtesy does not permit revealing the email addresses of others by such broadcast mailings."

(My mailing, of course, moved all the addresses to the BCC box, as is proper, so they each thought they'd received an individual message.)

It doesn't do much good, although in one case the original sender did comment about receiving "some feedback" about the mailing list. That particular spammer did NOT change her habit of sending the same kind of stuff in the same way, although she seems to have moved our addy to a "more selective list" so that we get a bit less of it from her.

John