The first two authors of that paper (N&G) in fact have a 2015 book on roughly the same thing. One can look at book reviews for this book too for (others') takes on N&G's hypotheses/research. For example, one review says:
The authors are at their persuasive best
when they are explaining the origins of the divergent confessional cultures in the Reformation and their significance in the postwar integration process. The argument becomes harder
to sustain in light of European secularization
and the diminishment of the institutional barriers that historically divided Protestants and
Catholics. While they acknowledge the importance of these trends, the authors are left having
to explain some developments that seem counterintuitive to their claim about confessional
cultures, such as the fact that leaders of the
historically dominant Protestant churches now
largely embrace political integration (p. 296),
committed Protestants are more likely to identify with the E.U. flag (p. 339), and prominent Catholic movements in Poland and Ireland have mobilized against European integration (pp. 312–13). In short, confessional culture
might not be as monolithic or predictive as it
once was.
(Emphasis in original. Review by J. Christopher Soper, Pepperdine University.)
A more lengthy review of this book is also fairly skeptical on the level of importance one should attach to the observed confessional differences. This latter review, despite its length, mainly flags the issues with the claimed differences within the Protestant "culture", unlike the previous review which also flagged the inconsistencies within the Catholic community nowadays. However, this latter review is also useful in that in spells out that the confessional-divide approach to EU's problems is not common among researchers.
The background assumption of the volume is that the origins
and course of “the struggle for European Union” can only be
properly understood if the religious factor (to use Gerhard
Lenski’s question-begging term) is examined across time and at
some breadth and depth. Although this starting point is not
widely shared among students of European integration whose
focus has most frequently been on the role of ramified economic,
political, and administrative complications of the process, its
relevance has previously been forcefully argued by some sociologists of religion such as Jose Casanova and historians such as
Wolfram Kaiser. By combining the insights of a wide range of relevant sources, the argument is developed with considerable
acuity and force. The central thesis is, firstly, that the European
integration project was in its origins a distinctive collective product of the Christian Democratic leaders of largely Catholic population groups in the six original EEC countries that carried into
practical politics principles and commitments deriving from a
long history of Catholic social and political thinking. Secondly
and more controversially, the corollary proposition is argued
that many of the difficulties into which the project of European
integration has run, as it developed and expanded from the Coal
and Steel Community of the 1950s into the (now 28-member)
European Union, have arisen crucially out of cultural contexts –
especially Protestant “confessional cultures” – which have perennially failed to nurture the vision of the original Catholic-inspired
project. The complex history of the emergent content of
Catholic and Protestant cultural biases, including divergent
commitments to the sovereignty of the Westphalian nation-state
as well as some of the underlying theological and ecclesiological
issues, is not underplayed. Given these central theses, it is
understandable that the authors concentrate on the dyadic
Protestant-Catholic differences rather than the admittedly
secondary role played by Eastern Orthodox and Islamic traditions and confessional cultures. Though these religions have
complicated the picture in the most recent decades, to have
dealt with them with anything like the same level of attention
would have overloaded the volume.
The overall argument does not rely on some proposition that the
whole enterprise was (let alone is [emphasis in original]) some Catholic plot set on foot by
the Vatican or high church officials, as the more extreme Protestant
objectors aver; rather, it documents the case that the key promoters
of European integration in the decade after 1945 (the politicians
Schuman, Adenauer, and de Gasperi in particular) were not just
Catholic by background, but also inspired by commitments particular to Catholic confessional culture and supported by parties whose
electoral strength during the early critical period relied in large part
on the Catholic vote. Furthermore, despite the rapid secularization
that has taken place over subsequent decades in most of Western
Europe in particular, the legacy of division arising from the
Reformation continues to resonate: while nativist anti-Catholicism
has declined particularly with twentieth-century ecumenism among
the middle classes, “class and culture divide the citizens of
Protestant countries into two groups: the mildly Euroskeptical, and
the rabidly Euroskeptical” (p. 341). This is admittedly something of
an exaggeration, but the argument is pressed, using recent research
on questions of political identity, right up to the book’s penultimate
sentence: “the persistent cultural differences across the Continent
make it impossible to achieve full political union of all the
European states” (p. 344).
(Bold emphasis mine. Review by: John T. S. Madeley, London School of Economics and Political Science.)
