A high number of those drawn to social work in those days were definitely drawn to the work by exposure to socialist concepts. As Yiddish speakers, the social workers were often the first Americans that a Jewish immigrant had contact with, the first to explain the American system and the first to teach the newly arrived how to speak English.

Rick,

True enough, but doesn’t that explanation just move the phenomenon back one step? Namely, why were those drawn into social work by exposure to socialist concepts Yiddish speakers (and therefore presumably Jews themselves)?

The same sort of argument could be made for the political uniformity of many immigrants (which, as you pointed out, explains the strongly Democratic leanings of first-generation immigrants). But few other groups went in for socialist politics with such enthusiasm, and it’s never been clear (to me, at least) why.