Anyone is free to join the religion if they desire for whatever reason. However, Catholicism at its core must be attached to a cultural identity, especially in America. You may be somewhat right with Benedict as that he is from Bavaria which does have quite a few Catholics so it might have a local Catholic identity, but for descendants of immigrants to have an attachment to such a particular region of their home nation is odd. I understand Phil and myself and many others remain attached to Napoli, but that is a bit more unique in the sense that a huge portion of the immigrants are from there and neighboring towns. Even if descendants were to lose that eventually, they'd still have the national identity of Italy which remains Catholic. Germany is just a mush-up of a hundred different things in the center of Europe. It is a bit telling that Benedict is the only German pope since Martin Luther.
There are several heavily Catholic regions in Germany outside Bavaria, and these regions up until not too long in the past, and certainly up to the point the ancestors of German-Americans left Europe, placed a heavy emphasis on them being, as Catholics, different from the Prussian (and others) Protestants. The Augsburg Peace and the principle of
cuius regio, eius religio had such a long lasting impact that basically up until World War II Germany was sharply divided between near fully Catholic areas (Bavaria, the Palatinate, Baden, the Rhineland, the Saarland) on the one hand and near fully Protestant areas on the other (Prussia, Saxony, the whole North and East). Secondly, I'd guess a few people with a German background have ancestors that originally came from Austria, but who would at the time of their migration obviously think of themselves as Germans; while being just as Catholic as any Italian or Irishman.
I do find that discussion quite interesting; and I agree about your views on the correlation between Cultural Catholicism and ethnicity. While I have obviously little to add on that in regards to America, I can say that this is also very much a thing back in Europe - in the sense that there is a Cultural Catholicism to several areas (Spain, France, Italy, Austria, Poland, Ireland) that does not necessarily correlate with actual exercise of beliefs.
