Please explain

Zachary states that people who believe a course of action to be morally obligatory for them have both the right and the duty to pursue that action and that no on else has any right to stop them from doing so. In response, Cynthia brings up an example that shows that Zachary's explanation is contradictory: "an artist who feels morally obliged to do whatever she can to prevent works of art from being destroyed confronting a morally committed antipornography demonstrator engaged in destroying artworks he deems pornographic." This scenario deems Zachary's statements contradictory since it would mean that the artist simultaneously has the right and duty to stop the destruction--since she feels morally obliged to do whatever she can to prevent works of art from being destroyed--and also has no right whatsoever to stop it--since the demonstrator feels morally obliged in destroying artworks he deems pornographic and Zachary stated that no one else has any right to stop one with a moral obligation from fulfilling that perceived moral obligation. Thus, answer choice (C) is our answer: "Zachary's principle is untenable on its own terms." Hope that clears things up! Please let us know fi you have any other questions.

Hey LSAT max staff, Can you explain why D would not be correct? I honestly did not choose the answer because I thought it was one hundred percent correct, I used the process of elimination to get the choices down to D and C and subsequently picked the wrong one. Thanks in advance!