When you read articles like this giving credence to beliefs that police in some European nations cannot be trusted to protect citizens from migrant criminals...
Police in Sweden accused of hushing up asylum seeker assaults at festival - Telegraph
You start seeing things like this...
Germany protesters demonstrate in Leipzig over influx of migrants | Daily Mail Online
If a nation's people see their elected officials failing to enforce the law, then some of them will take the law into their own hands and enforce it in their absence. It isn't fair to those immigrants who are innocent; they suffer as much from the indifference of the political class as the natives who are primary targets of the thuggish element who have been allowed inside. Both innocent elements of the equation, native-born and foreign newcomers, deserve better than a government refusing to enforce the law out of some fealty to ideologically-driven political correctness.
The middle-ground is to actually vet those who want to come into the nation and be highly selective in the process. A nation can benefit from immigration. But no nation on earth has ever benefitted from invasion by a mass element who hold their culture and society in contempt . Germany, Austria, Sweden, France, and others have merely submitted to invasion and are inheriting the maelstrom because of it. Those who have been intelligent regarding the process are those who have placed the emphasis on protecting the interests of those people who already reside within their borders.