Causing no issues is not the same as successfully integrating. As for there being plenty of communities who cause no issues, equally there are plenty who do cause issues. There are plenty of people who never commit a crime, then there are some who do. Should we also say crime is a smokescreen, not a problem and move on? Calling it a smoke-screen ignores the problem. Besides you only get to see the real underlying problem when things get a bit uncomfortable for the 'indigenous'.
Not your point tomorton, but I also don't agree the country is full. When I look at London and it's 9 million or so people and I know that there are cities coping with decent transport etc with 20-30 million people, it's hard to say even our biggest city is 'full'. It does 'feel' like there are too many people when you're stuck on the tube, or the house prices are crazy, but that's just bad transport planning and bad house building policy.
But what do you mean by integration? Bearing in mind any valid definition must be one that does not impede anyone's liberty to live as they choose as long as this is without harm to their neighbours.