If their goal was to bury it in mediocrity, I think that would be a good strategy. But I think their goal is to bring attention to a movie that distorted history in a meaningful way, then down-voting it is a pretty effective strategy. If you can down-vote it to the level where it has the worst score in the IMBD, or even among the ten lowest, it attracts attention and goads curiosity about what makes the movie so awful, which leads people to Google it and quickly find information about this social movement.