Prof. Stark is not on the "loony fringe," but is rather in the mainstream among the International Law community. That community's members tend to oversell International Law, and thus their own importance, in a fashion that is unsurprising in light of human nature.
I was afraid you'd say that. I so do want to be good and liberal but the liberals sure do make it hard sometimes.
I think, given the state of First Amendment jurisprudence, that there is no way the United States could have ratified the treaty without taking the reservation that it did. Whether the law ought to be that way is another question, but the language strikes me as ridiculously overbroad.