He has clashed with a number of anti-spammers, which has led to multiple terminations of online services that he's used--his DSL connection as well as web hosting. He has characterized this as mugging and assault as well as censorship. (Here is a list of some of Carlson's domains blocked by rhyolite.com for sending spam.)
In August, he filed a lawsuit (PDF) in Arizona Superior Court (CV2005-052008) against Robert Poortinga, his own providers who had terminated service, and Missouri Freenet Corporation. In his complaint, he argues that Poortinga and others have defamed him by calling him a "spammer" and accusing him of sending "spam," on the grounds that his emails do not meet the criteria in the CAN-SPAM Act.
"Missouri Freenet Corporation," named as a defendant in Carlson's suit, doesn't actually exist--the person he's intending to sue is Alif Terranson (on whose site the above lawsuit complaint PDF is hosted), who is a well-known anti-spammer and formerly ran the abuse team at Savvis. Terranson has supplied Carlson with information about how to properly name and serve him.
Carlson's complaint appears to me to be without merit. His argument based on CAN-SPAM fails because that act does not define the term "spam," which is a well-known term of art in the Internet world, not a legal term.
"Spam" originally meant bulk postings to Usenet newsgroups (an action associated with a couple of immigration attorneys also based in Scottsdale, Arizona), but quickly came to mean unsolicited bulk email (UBE)--email that is both (a) not explicitly requested by the recipients and (b) sent to multiple recipients. Although the most common form of UBE is unsolicited commercial email (which is what CAN-SPAM regulates), UBE and "spam" are broader than UCE and can include religious spam, insane spam, etc. Internet RFC 2505 endorses this broader notion of "spam," as does this definition from Spamhaus.
Although there are no legal penalties for spam that falls outside of what is regulated by federal and state laws (or laws in other countries), most online providers have stricter guidelines than what the law requires as part of their Acceptable Use Policies (AUPs). Customers of online providers are contractually bound by those AUPs, and can find their service terminated for violations even if they haven't violated the law. This has been the case since long before CAN-SPAM went into effect.
Another form of social penalty for spam is having one's email blocked by those who operate mail servers on the Internet--companies, organizations, and individuals have a variety of tools which can be used to block the vast quantities of unwanted email being spewed out daily by compromised machines as well as by those operating in a more aboveboard manner. Included in those tools are the ability to block by domain name or using IP-address-based blocking lists. What Carlson calls censorship is really just the owners of private mail servers setting rules by which their property may be used by others. (The issue is a bit more complicated in the case of an ISP, but so long as the ISP accurately informs its customers of what they've signed up for, they can apply filters consistent with their service. In general, ISPs want their customers to receive what the customers want to receive, as blocking wanted email leads to complaints.)
I'll keep tabs on this suit as it progresses (if it does).