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Any society needs the immigrants to be assimilated. Only Western culture tries to define assimilation as a bad thing. Every other culture want (and sometimes forces) foreigners to assimilate.
This does not mean that they have to change their religion or to be a clone of their neighbors. But this does mean that you must accept the basic values of the society. For example, in the Western world, democracy, human rights, freedom, tolerance and gender equality. You accept the law and the rules of your country. You accept the language as one of your languages. Nothing more but nothing less. Sometimes this takes a generation but it is eventually done.
This is not bad: is good so you end up with an unified country instead of communities fighting with each other. As an European citizen, I admire America for having done that. America has been successful because immigrants have assimilated. There are no German, Norwegian, Irish or Italian: they are American. Of course, Norwegian can preserve their pristine culture in Norway but, once they are American, they must assimilate.
You don't assimilate and you end up with a society like the ancient Yugoslavia: a patchwork of different ethnicities angered to each other. There were Serbs in Macedonia: their families have been centuries living in Macedonia, but they were not Macedonian: they were Serbs because they were unwilling to assimilate. The grievances accumulated between both communities were deep and the anger was big. Who needs that?
In Europe, Muslim people who are not assimilated are demanding to be judged by the shari'a, the Islamic law, where a female witness is worth a half of a male witness. This is not assimilation. If they want to do it in their countries, it is another thing. But every immigrant should be assimilated.