Opponents of open borders argue that, beyond a certain low rate, immigration creates assimilation problems. At a very low rate of immigration, it is relatively easy for immigrants to assimilate into the mainstream culture. At a higher rate of immigration, however, assimilation of immigrants becomes harder, particularly if the immigrants are able to assort solely with others from their own country and can get by with minimal interaction with natives.

Some categories of assimilation are:

• Linguistic assimilation: A concern is that immigrants, and even their children, may choose to live in enclaves that are largely populated by other immigrants from the same source country. Thus, the majority of them may well be able to get by using the language of their source country and they don’t need to pick up the language of the country they are now in.
• Emotional assimilation and patriotism: Immigrants may have problems assimilating emotionally with their new country because their loyalties are divided between the two countries.
• Political values and beliefs: Immigrants may not share the political values of their new country, and may not assimilate to these beliefs over time. See also political externalities.