The earliest opposition to Zionism by necessity were Jews because that community is where those original discussions happened.
And Jews still are the biggest critics of Zionism! There is nothing inevitable about Zionism becoming the expression of Jewish self-identity. Zionism became the dominant model for Jewish self-conception because the other models, such as Bundist Doikayt, were exterminated in the Holocaust. In that sense, Jews rediscovering extra-Zionist Jewishnesses is a reaffirmation of the breadth of the Jewish experience that was stolen by the Nazis!
And Jews still are the biggest critics of Zionism! There is nothing inevitable about Zionism becoming the expression of Jewish self-identity. Zionism became the dominant model for Jewish self-conception because the other models, such as Bundist Doikayt, were exterminated in the Holocaust. In that sense, Jews rediscovering extra-Zionist Jewishnesses is a reaffirmation of the breadth of the Jewish experience that was stolen by the Nazis!