Any film buff worth his or her salt is able to look at a movie like Triumph of the Will or Birth of a Nation and separate the objective craft from the thematic intent, with each of these considered in the context of the time, and further separate the entertainment value of the film, both for its original audience and for a modern viewer. The film buff can therefore recognize where a movie may carry creative and/or technical innovations, and trace those innovations down to other movies influenced by the original.
Most movie viewers are not worth very much salt.
These movies should absolutely be viewed and discussed by people with the knowledge, skills, and perspective to understand them. They should be taught in film classes to people who want to acquire said knowledge, skills, and perspective. They should not, however, be referred to as “great” because of the squishy connotations of the word. They should be described as “important” or “significant” with their problematic elements fully disclosed and conceded.
For people who judge whether a movie is “good” or “bad” solely on the basis of whether or not they found it entertaining (or, worse, make a value judgement about the movie by arguing whether other people should be entertained by it), films like these have no value and should not be watched. To claim a movie is good or bad based strictly on its entertainment value is just as ignorant and reductive as to say a Kandinsky painting is good or bad based on whether or not it’s pretty.