There are lots of Zionisms out there. (Wikipedia lists Labor Zionism, General Zionism, Revisionist Zionism and Religious Zionism; I can think of a few more flavors besides.) I think all Zionists consider themselves ideological supporters of Israel in a respect that they identify as important; besides that, they have surprisingly little in common.
For example, some Zionists believe that diaspora Jews should immigrate to Israel; others believe that Zionism has nothing to do with non-Israelis. Some Zionists focus on agriculture; some connect Zionism to big industry and investment; some understand it as confined to the political realm. Some Zionist ideologies (like mine) demand withdrawal from the territories and dismantlement of the settlements... but those settlers live according to a Zionism that says different.
Why do I consider myself a Zionist? Two reasons:
- Ethnic Jews are still not safe in much of the world. I think it is important that the global community protect freedom of movement for people born within oppressive regimes. One solution is a state which offers special rights to persecuted people (particularly, rights to quick citizenship and benefits for new immigrants). A state which offers these sorts of rights to ethnic Jews is a Jewish state.
Israeli law facilitates freedom of movement for diaspora Jews by offering all Jews a unique cluster of rights, largely designed to ease their absorption into Israel's national community. Because I think this is a good (though of course a non-optimal) solution to the problem of global antisemitism, I support the existence of a Jewish state. This is a Zionist claim.
- Alongside my abstractly pro-Jewish-state committments, I also have a more concretely pro-Israel committments. I identify with Israel in a way that engages me personally in the shared project of improving Israel. Let me explain what I mean by that.
I have a non-optional commitment to improving the United States, by virtue of my being a member of this national community — particularly, one with lots of undeserved political & social power. Although I am a citizen of Israel, I think that my personal involvement in the improvement of Israel is (more) optional, because I am not quite a member of the Israeli national community. The fact that my identification with Israel overextends my membership in the Israeli national community makes me a Zionist. (It also fuels my commitment to justice in Israel, and thereby, to a political stance that many people would label anti-Zionist.)