Capitalism is all about privatizing the profits, while socializing the costs. Email spammers have hit on an advertising medium paid for by others: the Internet. They send out millions of emails, and the recipients pay, through their subscription fees, to receive them. It’s not like sending junk mail postage due, it is sending junk mail postage due. Some big ISPs are a huge part of the problem, notably Pacific Bell (hence the spam-pink banner ad below).
If you’re tired of sifting through pyramid schemes and ads for hardcore bestiality porn in your email, there are several options. My personal favorite is SpamCop, a service that lets you quickly and easily analyze a spam email, get past all the forgeries and misdirection to reveal its actual source, and complain to the appropriate ISP. With reputable ISPs this results in the swift cancellation of the spammer’s Internet service, reducing the problem at its source just a little. There are some other anti-spam pointers elsewhere on this site.