That's right, I got Bar Mitzvah lessons and indoctrination in Mao's teachings all at the same time. I remember those days fondly because at the end of the lessons, we always got milk and Gentile blood cookies. Also a tradition.
Not all Jews have been leftists, and not all are today, but it is not deniable that leftism has been very strong among European and American Jews for the last 100 years and more. I do view it as a tradition that has been handed down from generation to generation in a very large segment of Jewish society. Perhaps since during the last 30 years or so, Jews have been allowed more access to American society, many will abandon their left wing tradition, and move to a more traditionally "liberal" one. OTOH, other Americans seem to be giving up the old "liberal" tradtions with which the country was started.
I use the word cherish, and find it appropriate, because my view is that Jews hold to leftism in the belief that it will benefit humanity. Tikkun Olam, repair the world, as my rabbi used to say. FWIW, the top guy at the Hebrew School where my kids went was pretty much of a socialist, though I don't think they spoke of gentile blood or anything. The rabbi was an avowed leftist, but a good man who meant well in spite of that.