The criticism had to do with wanting to restrict the term to its specific original context, a longstanding vicious lie about the Jewish people. The result of the criticism is that now when someone searches the term "blood libel," they see Sarah Palin, Sarah Palin, Sarah Palin. If the intent of the criticism was to preserve the purity of the reference, it's had the opposite effect. (If the intent of the criticism was to take advantage of a perceived opportunity to take another shot at Sarah Palin, the hypocrisy is too nauseating to describe.)
Meanwhile, Rabbi Shmuley Boteach says "Sarah Palin Is Right About 'Blood Libel.'"