Laurence Canter, one half of Canter and Siegel, the Internet's first large-scale commercial spammers, on email spam:

(CNET)

To some extent, we probably welcome advertising. The problem with the incredible volume of unsolicited e-mail that we get today though is that, unlike junk mail that you receive in your snail mailbox, it's not immediately apparent that something is junk mail. With e-mail, you have to at least read the subject or who it's from to determine that it's junk and you don't want it. And the fact that it's so easy and, for practical purposes, costs nothing to send is resulting in considerably greater volume.