[inglor_cz]

Too many exceptions from this rule.

Vienna is pretty mixed since the times of the Austro-Hungarian empire, but fairly safe. Glasgow is almost purely Scottish, but dangerous. Naples is probably less ethnically mixed than Rome, but more dangerous. Marseille is a lot worse than Genoa etc.

I don't doubt that particular kinds of immigration can worsen crime situation considerably, but some places can manage that and some fail miserably. You can even see it in the same city if the political representation changes. AFAIK the current mayor of Barcelona is notorious for letting street crime fester.