A couple of years ago, a well-known internet marketer tried to get a new account with several auto-responder services. He wanted to import one of his mailing lists and use the service. None of the major auto-responders would accept the list because he would not divulge its origin.
Emailing people who have not opted into your list is considered spamming, though not strictly by the letter of the law, which only requires a way to opt-out. I get spam mail every day and the people that send spam are getting more and more sophisticated. They can even come to my server, capture my email address, and send me an email as if it were coming from me. Obviously, people sending spam are making sales and that's all the justification they need. They will keep on spamming forever as long as people keep buying male enhancement products or calling their 1-900 numbers... unless technology stops them. Besides the aggravation of spam, there is also the threat of technological terrorism and the spreading of computer viruses.