I’m a jewish voter and I have this argument with my jewish friends all the time. They hate Israel as much as the palestinians do, as much as the left in this country hated the country under Bush.
I think they believe if they distance themselves from Israel, the radical left will see them as friends and not go after them, too. It's a case of self preservation.
They've forgotten one very important fact - they're still Jews, and the left hates Jews.