I'm not sure having multiple cultures in a country is necessarily a bad thing but it can be a mistake not to be able to recognise the issues or treat people accordingly. Like Singapore is a successful very multicultural society but if immigrants/expats do bad stuff they get kicked out rapidly.
At least he has the honesty to say that he doesn't have a fix and that some of the proposed fixes aren't going to work.
I think if Europe hadn't been an abusive colonial power over much of the rest of the world for centuries, then this whole immigration question wouldn't figure so prominently in recent times.
What has colonialism to do with the aftermath of 1970s/1980s Turkish, Pakistani, and Arab immigration to Denmark and Germany?
Western colonialism/interference, combined with western religion, is the root cause of most, if not all, of the problems in Africa and Middle East.
I’d provide references, but the easy solution is going to a library and reading.