Use Google, and you'll see many people asking whether Julian Assange is a reporter, and therefore protected under the first amendment. Such as "Why Julian Assange is a journalist - And why WikiLeaks is entitled to the same First Amendment protections as the New York Times ". And you will also find people responding to the implied argument, like Reason magazine.

No one has explicitly said the First Amendment should apply only to journalists. But posing the question "Is X a journalist, and therefore protected by the First Amendment?" has that implication.