[xenophonf]

  It was my understanding that 18
  U.S. Code § 871 included depictions
  enticing or encouraging such acts.

Not according to Brandenburg v. Ohio, which states:

  The constitutional guarantees of free
  speech and free press do not permit a
  State to forbid or proscribe advocacy
  of the use of force or of law
  violation except where such advocacy
  is directed to inciting or producing
  imminent lawless action and is likely
  to incite or produce such action.

The key words there are "incite" and "imminent lawless action". But don't just take my word for it. You can read the decision for yourself here:

https://www.law.cornell.edu/supremecourt/text/395/444