 However, Dworkin thinks, considerations of offense may provide some justification for preventing or restricting the public display of pornography so as to avoid its causing offense to non-consenting adults who might otherwise involuntarily or unwittingly be exposed to it. Joel Feinberg, another well-known liberal defender of pornography, agrees. But Feinberg thinks that such restrictions must be justified by a principle other than the harm principle, for he thinks that certain sorts of unpleasant psychological states are not in themselves harms. Feinberg calls this additional principle the offense principle. The offense principle says that “It is always a good reason in support of a proposed criminal prohibition that it would probably be an effective way of preventing serious offense (as opposed to injury or harm) to persons other than the actor, and that it is probably a necessary means to that end (i.e., there is probably no other means that is equally effective at no greater cost to the other values)” (Feinberg 1999, 78; for a more detailed discussion, see Feinberg 1985).