I just dont think this is completely accurate. Jews are notoriously Democratic, but oddly enough, they are not notoriously pro affirmative action. The data show that Jews are only lukewarm towards it, and there has reportedly been considerable tension between black and Jewish organizations over the perception that the latter are not supportive enough of AA.
A number of Jews have been the movers and shakers behind legal challenges to AA: for example, Alan Bakke and Carl Cohen. Bakke was the medical student who brought the first case challenging his rejection by UC in order to accommodate a far less qualified black applicant (who not incidentally went on to eventually kill a patient and lose his license). Cohen is a U Mich professor and former ACLU official who has been fighting AA for years.
Jews tend to have a very deep respect for merit and accomplishment, and I think this explains why a lot of Jews bristle at AA despite their otherwise liberal sentiments. Of course this is just one of many reasons why such Jews should say goodbye to the Democrat Party. I'm still working on it.
They were also damaged by Jewish ceilings at a lot of elite universities in past decades (much like those imposed on Asians now), which also explains their frequent skepticism of affirmative action.