This is a bit “english” (polite) and “american” (upfront) at the same time…
Normally, if I get spammy cc-the-world mails from people I rant about how they are human spam-virus propagators. They tend not to do it again, but equally I don’t have as many friends as I used to 
This is a bit more polite, personal and – well – it’s just quicker than the effort of being nice…
Best of all, the effort of saying “stop it or meet my spam filter’s blacklist” is now roughly equivalent to the time they took to spam you in the first place. Balance. Zen.