Every vote sends a message. Last week, when the Berkeley Jewish Student Union voted to bar J Street's student organization from membership, the message it sent was regrettably clear:

The choice is up to you - You can be welcomed as a Jew, or you can speak your mind on Israel.

Now Berkeley, so often ahead of the curve, has distinguished itself once more. Its Jewish Student Union, founded expressly to provide a forum for communication and to unify campus Jewish organizations, has become the first such group in the country to have denied membership to the unapologetically pro-Israel, pro-peace J Street U.

Trends matter. The Berkeley vote lends momentum to a wider tendency - the exclusion, over political tensions, of more and more Jews from the already shrinking tent called the American Jewish community.

Places like Berkeley matter. It was in Berkeley and other like-minded towns that a surprisingly large number of young people forged a lifelong commitment to work for the ideal of an Israel true to values of democracy and prophetic justice.

It was in places like Berkeley, with its tradition of respect for universal rights, where they learned that support for Israel need have nothing to do with support for occupation or settlements or defaming Palestinians or refusal to compromise. That support for Israel could have everything to do with support for strengthening democracy there, freedom there, equality there, and genuine self-determination for both Jews and Palestinians.

It was in places like Berkeley, with its tradition of activism and freedom of expression, where they learned that there is no contradiction in being critical of Israel's failings while acknowledging its merits and dangers, and believing in its potential.

It was in places like Berkeley, with its tradition of coalition-building, where they learned that Israel needs all the help and support it can get.

What Israel does not need, is a decision which cuts that support.

In a place like Berkeley, it takes guts for anyone, whatever their politics, to admit that they care about Israel. If their politics are progressive, if, like the J Street U people, they explicitly oppose both the occupation and the Boycott, Divestment, Sanctions movement, one of the voters in the Jewish Student Union decision may take the trouble to denounce J Street in the Northern California Jewish newspaper as "anti-Israel" and, perhaps most damning, not "part of the mainstream Jewish community."

What remains unclear is why, when Jews in Berkeley boycott fellow supporters of Israel, they believe that they are doing Israel, or the Jewish people, any good.

Does the Berkeley vote truly reflect the kind of community that Jewish students at the University of California want? An intellectual ghetto, walled off from debate, bricked up against nuance, a trompe l'oeil of democracy, of openness, of communication?

Here in Israel, the war that is closest to us, the war that threatens us most directly, and perhaps, most permanently, is a struggle over exclusion. It is a war which, week by week, vote by vote, uses democracy to diminish democracy. One which, edict by edict, uses the institutions of Judaism to alienate and repel Jews, and the institutions of Zionism to alienate and repel supporters of Israel.

Every vote sends a message. It can build bridges, or burn them. It can foster communication, or deter it. For many people who have lived in Berkeley, it was in part because they found a welcoming, open, questioning, courageous, progressive community of Jews there, that they made a decision to come to Israel to live. Most, wherever they are now, are still actively working to make this a much better place.

To the members of the Berkeley Jewish Student Union, just this: Take a moment. Do something for your community, and for Israel. Vote again.