Assimilation is the key- and it's when the newcomers do not issues are raised. For example it's hard to have a safety net of low income gov help when the many groups view this "safety net" differently. One group may view it as a safety net when a person is down on their luck to be used then and only then and another group views it as a base income that is a right to collect $ from the gov regardless of if you can work or not. One group may view standing in line as a basic rule of society- the other does not and everyone rushes forward with the strongest outreached hand getting the "prize" first. Without assimilation society truly becomes closer to law of the jungle style of living and everyone is weakened. Another simple everyday example is what side of the road a group rides bicycles on. In the USA the law and rule is to ride with traffic on the right side. Hispanics and illegal immigrant nearly 100% ride against traffic- causing traffic accidents that simply would not happen if assimilation took place. It's a very small thing but shows how culture and society is weakened- there are literally thousands of examples, and many of those examples are reasons the culture/people ask that outsiders to assimilate and if they do not, to leave.