I generally agree with the moral principle "treat others the way you would want to be treated". I personally think the stance on morality you describe is propagated by people who want to be more than human (consciously or not). Paradoxically, they are expressing a human desire in doing so. This is why their philosophy is paradoxical as well. Because we live in a reality where we are human, we have to accept the limits of humanity in understanding all the questions we ask ourselves.
I'll say it again. Insofar as people within the movement (who we can collectively call "the movement") ascribe absolute, inherent moral values to things like freedom, and at the same time maintain that moral values are subjective and not objective, you can say there IS a contradiction; however, if this same conglomeration of people are simply saying: "if you like freedom like I do, then think about things THIS way; if you don't, fuck it," there is no contradiction. And, for the last time, since a "movement" is a fiction, like a corporation, you really have to assess the motivation of its constituents. Some people might look at it one way, some people might look at it another way. No one really has ownership of a meme like "post-modernism." One person might say it includes the concepts that freedom is something objectively good, another might disagree. Neither is right or wrong, because, once again, meaning and values (in this case, the meaning of a word) are projected from the subject to the object (in this case, a meme like "postmodernism"). Good luck with your paper.
Never assume anything. I am writing no paper. The quoting I did was because I am careful to give credit to where I got my ideas. I don't claim that there is anything new under the sun. Also, I am a librarian, which makes me very careful.