The headline of this article by Hirsi Ali and Daniel Huff is unfortunate because it distinguishes one particular offensive group. But the authors do in fact acknowledge others and note that the case of anti-abortion Christian Extremists has been partly addressed by legislation in the US. Unfortuantely the Freedom of Access to Clinic Entrances Act is very narrowly focussed and Hirsi and Huff argue that a similar act is needed to protect against threats intended to constrain otherwise acceptable free expression. But I would go further
In fact what is needed is a more global approach to the issue of coercion by threat of violence which should include both of the above as well as intimidation of witnesses and any other utterance or advocacy of extra-legal violence and it should be established that the communication of such threats is the only kind of communication that is not included in any right of free expression.
In the meantime, acts of (self?)-censorship such as the one complained of here become questionable as to their motivation. Is it a possibly admirable wish not to give unnecessary offense or a craven fear of retribution which would justify the withholding of a cartoon which mocks the prohibition of certain images without actually violating it?