Allowing someone to steal pennies a day adds up to real money if hundreds of thousands do it to millions of people. Erol's has had to upgrade their mail servers 3 times in the past 1.5 years, due in large part to the excessive amounts of junk email received en toto by Erol's customers. And since email servers aren't cheap, we've had to raise our prices, which means our customers are subsidizing advertising that they don't want. Furthermore, this applies across the board, so customers who have never received any junk email at all are still helping to defray the costs of the ones that do. Spammers WILL stop.
Nobody doubts that.
The only question is whether they will do so before or after destroying the net, like any other parasite that dies after killing its host. That last lie has led to several divorces, several firings, and at least one suicide. Lies have consequences. My on-line mailbox can hold a maximum of 50 email messages. By invading my mailbox with unsolicited advertising, the spammers are capable of depriving me of the email I desire receiving.