So let's say you care about Jews (unlike the end-times Christian Republican support of Israel, which has nothing to do with Jews as Jews and only cares about Jews as pawns in their Christian worldview); and let's say you've realized the ahistorical (i.e., bullshit) nature of the arguments about Jewish authenticity that underlie a certain pro-Zionist argument.
That is, we reject the argument that you can only really express your Jewishness in Israel; but conversely, that doesn't mean that my brand of Jewishness--bagels, Woody Allen, shiksa girlfriends--is more authentic. (My brother and I are both our parents' kids, but we've developed differently. Is one of us more authentically inheritors of our parents' legacy? In order to answer that nonsensical question, you'd have to define what our parents' legacy was, which would be a process of highlighting certain aspects and downplaying others--and who's in a position to make that call? Authenticity-search is a game with no winners.)
Which is why, if some people feel the need of Zion to express their Judaism, then more power to them. In that way, I'm a Zionist. Bet you didn't see that one coming.
But I'm a limited Zionist, a two-state Zionist. Because if you claim the right of self-determination (as Zionist Jews do), then you have to accept the right of other people's self-determination, like the Palestinians.
(Which is why Newt Gingrich and others like to refer to the Palestinians as an "invented" people--he can accept self-determination ("a People should have a homeland") and still deny it to the Palestinians ("not all people are a People").)
The concept of Zion-for-Jews relies on self-determination; and no self-determination can overpower another person's self-determination. (That is, your self-determination can't include subjugating another people's.) Which is why the only coherent Zionism these days is for a two-state solution.
Or for a single state that treated everyone equally. Because, honestly, Kosher and Hallal can get along pretty easily (hold the yogurt sauce) and everyone likes falafel.