The sad reality is that the vast majority of anti-Zionists today are motivated by a hatred of the Jewish people - by a contemporary variation on classical antisemitism.
It is not always easy to distinguish anti-Zionists from antisemites, but there are some criteria that may be helpful.
From the beginning of political Zionism in the 19th century, there have always been anti-Zionists, even among Jews. Some were religiously opposed to the establishment of a Jewish state; others were politically opposed; still others were culturally opposed. There was Arab and Muslim opposition to any Jewish political entity in the region.
That was then. Since that time, the vast majority of decent people have supported the right of the Jewish people to self-determination, in the form of Israel as the legitimate nation state of the Jewish people. When Israel declared independence in 1948, it was recognized by all the major western nations including the United States and the Soviet Union. The left, both internationally and in the United States strongly supported Israel and Zionism. Only the Arab and Muslim nations along with their allies opposed Zionism.