For all of you "doorknobs";
ISIS (or any form of terrorism in general) has no free speech rights under the US Constitution. Speech that incites or conspires towards criminal acts is not constitutionally protected legal speech.
Billions of dollars in the US are transacted daily via the internet -- the internet will not be closed in the USA. Law enforcement can monitor internet communication for illegal activity and they do.
Demogogery PDF
Here is the manual for this sort of demagoguery -- Trump could of wrote the book ... Mein Kamf is also a good example of demagoguery's effectiveness.