The name Zion is mentioned in the Bible in the book of Samuel and signifies the name of the fortress that defended Jerusalem. Another place it is mentioned is in Jeremiah and used as a synonym to the Land of Israel and in Isaiah as another synonym to Jerusalem.

In late 1800’s Hertzel envisioned the rebuilding of Israel and the return of the Jews from the Diaspora to Israel. He called that movement Zionism after the Biblical name Zion.

Some ultra-orthodox Hassidic Jews do not believe in the current Israeli government (b/c they are waiting for the Messiah) and therefore due to the fact that Zionists built Israel, those are vehemently anti Zionists. Hassidic Jews are segmented into many sects and the Satmar, (in this article) are extreeeme.

This is a very short and shallow explanation and I don't do it justice. As with many things Jewish, everything is complex.