I think the difference is that it's more obvious that aliens in NJ are a joke. Armed men kidnapping children from schools in Mexico is an entirely realistic scenario that any reasonable person should expect to cause a panic.
It's almost like that but times have changed. In 1938 it was mainly a broadcast of a message which then wasn't easy to broadcast again by the people. Nowadays you broadcast something and in a couple of minutes it can reach the whole country just because of re-tweets and mobile messages. The end result can be a good number of times worse because of this.
Or maybe we should think twice about saying things like "your kids are being killed at school". I am open to suggestions but I have never heard about a book causing mayhem in a couple of minutes.
The reason why is that people don't expect to trust books. Open a random book at the bookstore, and it's probably a story that the author made up. Twitter is the same way, but people don't realize this yet.
I don't see why authors should be held responsible for their readers' stupidity, though.
That classic scenario originated in an opinion supporting jailing someone for handing out flyers opposing the WWI draft, during a period in American history when jailing people for antiwar speech or speech encouraging Socialism or Communism was frequent. It has been superceeded by law and decisions more in accordance with the First Amendment at least half a dozen times since.
The definition of free speech that that argument was used to defend was the Espionage Act of 1917 which:
o Made it a crime to convey information with intent to interfere with the operation or success of the armed forces of the United States or to promote the success of its enemies, punishable by death or by imprisonment for not more than 30 years or both,
o Made it a crime to convey false reports or false statements with intent to interfere with the operation or success of the military or naval forces of the United States, punishable by a maximum fine of $10,000 or by imprisonment for not more than 20 years or both,
o Made it a crime to promote the success of its enemies when the United States is at war, punishable by a maximum fine of $10,000 or by imprisonment for not more than 20 years or both,
o Made it a crime to cause or attempt to cause insubordination, disloyalty, mutiny, refusal of duty, in the military or naval forces of the United States, punishable by a maximum fine of $10,000 or by imprisonment for not more than 20 years or both, and
o Made it a crime to willfully obstruct the recruiting or enlistment service of the United States, punishable by a maximum fine of $10,000 or by imprisonment for not more than 20 years or both.
The Sedition Act of 1918 extended this to:
o Make it a crime to use "disloyal, profane, scurrilous, or abusive language" about the United States government, its flag, or its armed forces or that caused others to view the American government or its institutions with contempt, and
o Give the Postmaster General the right to go through mail and refuse to deliver any that did any of these things while the United States was at war.
This resulted in about 1500 prosecutions and 1000 convictions for speech, and the sentences were generally between 5 and 20 years.