LONDON — Ira Stup was raised in Philadelphia attending Jewish day school and camps. He found his home in the Jewish community and was “intoxicated with Jewish democracy” as framed in the ideals of Israel’s foundation. Now he has returned deeply troubled from a one-year fellowship based in Tel Aviv.

The worst single incident occurred on Ben Yehuda Street in central Jerusalem. Stup, 24, a Columbia graduate, was returning from a rally with a couple of friends carrying a banner that said, “Zionists are not settlers.” A group of religious Jews wearing yarmulkes approached, spat on them and started punching.

“About 20 people saw the whole thing and just watched. They were screaming, ‘You are not real Jews.’ Most of them were American. It was one of the most disappointing moments of my life — you can disagree as much as you want with a banner but to allow violence and not react is outrageous. For me it was a turning point. Nobody previously had said I was not a real Jew.”

The view that American Jews supportive of Israel but critical of its policies are not “real Jews” is, however, widespread. Israel-right-or-wrong continues to be the core approach of major U.S. Jewish organizations, from the American Israel Public Affairs Committee (Aipac) to the Conference of Presidents of Major American Jewish Organizations.