Is spam legal?
Maybe.
Part of the problem is that the explosive growth of the Internet, and the very recent rise of professional spammers, has moved much faster than the laws, or the knowledge of the people who are supposed to enforce them. For example, most people at the US FCC, which has jurisdiction over interstate junk faxes, don't even know what junk e-mail is, let alone how the laws they enforce apply to it. (The FCC's Consumer Litigation department can be reached toll-free at 1-888-225-5322)
Many people think that spam can be shoehorned into the provisions of the U.S. anti-junk-fax and telemarketer regulation laws (US Code 47.5.II), but to our knowledge this has not yet been tested in court.
There's a good chance that spam is illegal under various U.S. state laws. For example, a case has been brought against a spammer based on the Washington state junk fax law. The Washington law defines a telefacsimile message as "the transmittal of electronic signals over telephone lines for conversion into written text." Check your state law if you would like to sue a spammer.
In the U.S., everything not explicitly illegal is permitted. Until a court makes a decision, or Congress passes a law, spam may be legal here. However, there are plenty of precedents in common and tort law that find similar activities illegal. In a nutshell, spamming is theft of service, and theft is illegal without needing special laws.
In some countries, unauthorized use of computing resources is a crime. [If you know about legal issues with spam in other countries, please let us know!]
Another part of the problem is that many people want as little government interference in the Internet as possible. Although the Internet has its roots in a U.S. Government network, it is currently a cooperative coalition of commercial carriers. It is far better for the carriers to agree on the rules than for the government to step in and set up inflexible laws.
Yet another facet is the international nature of the Internet. If one country passes laws against spam, professional spammers will just move abroad, the same way that the phone sex lines moved to the Carribean after the U.S. regulations on them became too restrictive.