This article covers three situations in which anti-vaccine activists mounted unjustified, problematic attacks against critics, in an attempt to silence them:

A. Attempting to get Dr. Paul Offit fired over a comment about autism.

B. Threatening Dr. Emily Willingham with a lawsuit with no basis.

C. Attacking high school students who made a pro-vaccine film.

http://www.immunizeusa.org/media/52996/anti-vaccine-intimidation-daily-journal-may-14-2014-1-.pdf