"If people really thought about the issues, however, they wouldn't necessarily find spam any more invasive than other forms of advertising, like television commercials..."

I have to disagree. Free speech ends where my privacy begins. Commercials on TV, that's public media. Remember the furor over telemarketing? That is direct and private communication. People's objection was based om invasion of privacy, and legislation has signaficantly curtailed it. Junk snail mail was mentioned, and is often objected to; however, a concept of proportionality of burden comes to play. The junk mail originator has to expend a burden comparable to that the recipient expends to look at it and throw away; so it tends to be self regulating to a degree. Spam does not have this limitation. The spammer expends no effort, or cost, in contacting you and doesn't even know who you are. (The spammer's efforts are spread over millions of recipients) Each recipient must look at it briefly and delete it manually.