Two months ago, Tareq Mehanna, an American-born citizen from Massachusetts, was convicted of conspiracy to provide material support to al Qaeda, providing material support to terrorists (and conspiracy to do so), conspiracy to commit murder in a foreign country, conspiracy to make false statements to the FBI, and two counts of making false statements. He traveled to Yemen to get training in order to fight against American troops in Afghanistan, but failed. His use of the Internet to propagate Jihad, however, was defended by civil libertarians as "free speech," protected by the First Amendment.
But Jihad is not philosophy. It is a call to action, not meditation or self-examination. A central tenet of Islam, it can mean helping others and self-improvement. But for most Muslims it means a divinely mandated war against "infidels" – non-Moslems. It can take many forms: piloting planes into buildings, blowing up planes with hidden bombs, murdering people who are accused of insulting Mohammed and the Koran, and urging others to engage in violence – that is, incitement.
It is also incumbent on Muslims anywhere, anytime, and for any reason they personally feel applicable. Since Islam does not have a hierarchy of authority, although some leaders are more acceptable than others, one can pick and choose. There are basically no rules or restrictions. One can follow a local sheikh collecting charity, or a preacher exhorting homicidal attacks.