Is your first sentence true? If you think so--how do you explain the cultural differences between different parts of the U.S. with different immigration histories? I can't help but notice that Minnesota (heavy Scandinavian influence) and Massachusetts (heavy Puritan Anglo influence) are clean, low in corruption, and orderly, while New Jersey and New York (heavy southern Italian influence) are significantly less so--a characteristic that they share with contemporary southern Italy (e.g, Sicily).
It's also worth pointing out that the social infrastructure for assimilation that existed in the early 20th century has since been destroyed. Italians immigrated to a country where there was strong pressure to abandon their foreign culture and assimilate into Anglo norms, attitudes, and customs. Assimilation was also facilitated by restrictive immigration laws adopted in 1921, which dropped the foreign-born population from 15% to under 5% by 1970.
Even then, the evidence we have is that assimilation only worked about halfway: https://www.sup.org/books/economics-and-finance/culture-tran.... To this day, differences in social attitudes between European countries show up in U.S. descendants of immigrants from those countries: https://cis.org/Richwine/Still-More-Evidence-Cultural-Persis... ("For example, in Europe, Norwegians are more trusting than Germans, who are themselves more trusting than Italians. Despite over a century passing since their peak period of immigration, those three ancestral groups order themselves the same way in the United States: Norwegian-Americans are more trusting than German-Americans, who in turn are more trusting than Italian-Americans.").
It's also worth pointing out that the social infrastructure for assimilation that existed in the early 20th century has since been destroyed. Italians immigrated to a country where there was strong pressure to abandon their foreign culture and assimilate into Anglo norms, attitudes, and customs. Assimilation was also facilitated by restrictive immigration laws adopted in 1921, which dropped the foreign-born population from 15% to under 5% by 1970.
Even then, the evidence we have is that assimilation only worked about halfway: https://www.sup.org/books/economics-and-finance/culture-tran.... To this day, differences in social attitudes between European countries show up in U.S. descendants of immigrants from those countries: https://cis.org/Richwine/Still-More-Evidence-Cultural-Persis... ("For example, in Europe, Norwegians are more trusting than Germans, who are themselves more trusting than Italians. Despite over a century passing since their peak period of immigration, those three ancestral groups order themselves the same way in the United States: Norwegian-Americans are more trusting than German-Americans, who in turn are more trusting than Italian-Americans.").