Orin Kerr notes at Volokh.com that Kagan’s likely confirmation will mean that the Supreme Court will be entirely composed of Catholics and Jews, with no Protestant representation at all. Kerr has no overarching theory about this, except for the obvious one that Jews have been numerous in the legal profession and in liberal circles, and so it is hardly surprising that they would constitute the bulk of the Court’s left, despite their small numbers in the general population.
I agree; plus I would add that the Judaism itself has a long and illustrious legal tradition in general, from Leviticus to the Talmud and beyond.
But what about those Catholics? Kerr advances the following tentative idea, which sounds reasonable to me:
One possible hypothesis is that this is an indirect consequence of Roe. Given the Catholic church’s strong pro-life position, and the fact that Supreme Court nominees are not directly asked their view of such matters, affiliation with the Catholic church may be seen by Republican Administrations and conservative judicial groups as signaling a likelihood of a nominee’s view toward abortion rights while not providing any direct evidence that could itself cause controversy (given the wide range of views on abortion among self-identified Catholics).
So far I haven’t found any figures on whether Catholics are more likely than Protestants to go into law and the judiciary. But I note another statistic, most probably irrelevant but intriguing nonetheless: Jews and Catholics seem to have some sort of special linkage/relationship as compared to Jews and Protestants. It is a strange and little-remarked-on reality that Jews who marry Christians tend to marry Catholics disproportionately. The fictional “Abie’s Irish Rose” and TV’s “Bridget Loves Bernie” were popular demonstrations of this phenomenon. The Supreme Court appears to be no exception, although it’s hardly a love match between the liberal Jews and the mostly-conservative Catholics on its bench.
[NOTE: Here's a much more serious exploration of the Christian denominations of SCOTUS Justices thoughout our history, containing the following interesting facts:
Throughout the court's history, some groups—notably Episcopalians, Presbyterians, Unitarians, and Jews—have been significantly overrepresented in comparison to their prevalence in the American population, while other groups have been significantly underrepresented. Though Baptists constitute the country's largest Protestant group, there have been just three Baptist justices. The second-largest Protestant group, Methodists, have supplied only five. There has never been a Pentecostal justice, despite that movement's explosive growth since the Azusa Street Revival of 1906...
The mismatch between Supreme Court members and average Americans is in part an example of the generally non-representational nature of elites, even in the supposedly egalitarian United States. From the late eighteenth to the middle of the twentieth century, a white Protestant establishment held sway, as Congregationalists (the heirs of the New England Puritans), Episcopalians, and Presbyterians pretty much ran the country and the rest of America's Christians pretty much let them. Unitarians, who controlled Harvard, got to participate heavily in governance as well, despite the fact that most Americans considered them heretics. The revivalist traditions that caught fire in the nineteenth century, including Baptists, Methodists, and Disciples of Christ, rapidly outstripped the establishment churches in membership but never overtook them in terms of cultural power. Evangelicals, for the most part descendents of the revivalists, have enjoyed even less access to the country's most exclusive halls of power, including the Supreme Court, the Senate, and the presidential offices at Ivy League universities.
The makeup of the current Supreme Court also reflects trends peculiar to jurisprudence. Judaism and Catholicism have extremely long and rich legal traditions, while Protestantism generally, and evangelicalism specifically, does not. ]