When I practised Aikido, my master told us, Let your opponent hit where he wants to, then let him fall where he wants to. I would apply the same Aikido strategy with spammers. They send out tons of mails in the hope that one out of a thousand will click on a link. Let’s make them happy, let everyone click on the links. Plugins could be added to mail clients that processes each spam and clicks every single link in it. Spammers would get many times more clicks, they would need a larger infrastructure to cope with it, and a click wouldn’t mean an intention to buy anymore.