Unsolicited mass email is simply the equivalent of subscribing a lot of people at once to a mailing list they don't want to be on. And because these scam-artists trade their lists with each other it's not a one-shot deal and you can't get off the list... the next person to use your name never knows what you might have said to any other operator.
Not that these folks have any intention of doing so, if the experience of people who've sent in drop requests from made-up accounts is anything to go by. The best way to get subscribed to one of these lists is to ask to be taken off it, it seems.
If people are sanctioned for "social-engineering" tricks like subscribing strangers to regular mailing lists, why should these commercial mailers be held to any weaker standard of conduct? It's just a different form of mailbombing, horizontal instead of vertical, and has no better justification.
It's senseless. I've subscribed to commercial mailing lists before, on topics that interest me. Directed mail is more productive and no less expensive than carpetbombing everyone who posted to Usenet on a given week... unless your product is something nobody with an ounce of sense would buy. Which explains why most of these list operators are in the business, I guess.