Immigrant groups had their children learn English and assimilate because they wanted their children to prosper in America. However, they went to sometimes great lengths to preserve their cultures for their descendants as well by organizing their own private institutions to educate their descendants in the culture from the old country.
The 14th Amendment was written and passed by Republicans in 1868 to prevent state law and state courts from abusing free blacks, especially recently freed slaves. It failed. The Civil Rights Act of 1964 was passed to correct the failure. As long as the Feds focused on individual rights everything was fine.
Then the idea of identity politics and group rights became popular at the federal level. To further group rights, the Feds decided they need to intervene to preserve multi-cultural roots. But private efforts to preserve culture and government sponsored efforts to preserve culture are two entirely different things. The federal government is a one size fits all central government. When they favor one culture, they are seen as suppressing another. The federal effort to encourage "cultural diversity" began to look like an effort to favor some cultural groups at the expense of others. In particular, Evangelical Protestants felt like the government was trying to destroy their religion. Although, I am not an Evangelical Protestant, I think they have a very good case to make that they are being harassed by the government.
The Constitution does not say anywhere that the federal government is in charge of culture. It should not be involved at all. Rights should return to being individual rights, not group rights. People should try to be tolerant instead of spending so much time trying to be on top.