AFI and the idea of a "Great Movie"

I have a bone to pick with the American Film Institute over their movie selection process. AFI occasionally posts lists of "100 Greatest" in various categories of film. Recently they announced that they plan to do the survey again every decade or so due to “changing tastes.” What that says to me is that their list is not based on any objective criteria—it is merely what some people like. The AFI needs to establish some kind of criteria for a good movie—completely objective and not subject to whim and fancy. They need to base their lists on these criteria, and then each decade reconsider the list in light of movies that have been made since. Greatness should not be a matter of "Changing Tastes" but of unchanging values. The problem here is postmodernism. AFI has bought into the idea that there is no truth, only perspectives, and that we cannot set up external standards. In other words, “beauty is in the eye of the beholder” and we cannot say that any movie is really “better” since it is just a matter of whatever tastes and standards prevail. That is poppycock! It is postmodernism, pure and simple! AFI has lost quite a bit of credibility with me over this. Can't we set up an objective set of standards for a “great movie”? Perhaps we need different criteria for different movie genres. However, perhaps there is a core set of standards, and then certain genre specific standards that should be added in. I am not sure of the specifics, but I suspect that the whole idea that "changing tastes" should determine "greatness" is a serious error. "Greatness" should be a factor that helps refine and improve "taste" in movies as in music, art, theater, and literature.