text: The standard liberal, pro-free speech premise is that speech may be curtailed only when there is a clear and present danger of harm to others. The classic example is falsely shouting "fire" in a crowded theatre.
  
  But if an ISIS supporter urges on line for people to rise up and kill infidels, that's not a clear and present danger. That's a remote danger and so doesn't qualify for censorship under the assumed premise.