The issue was not diversity but rather the social welfare system and the governments failure to integrate migrants properly into the english system - which, in fairness, very few countries are good at. from viewed from afar its difficult to refute your argument, better to agree but note that there are some small exceptions. the quality of government is also a factor.
still, bruce lee does spring to mind. "I fear not the man who has practiced 10,000 kicks once, but I fear the man who has practiced one kick 10,000 times". if 10,000 ppl are doing 10,000 different things, no big deal. if 10,000 ppl are doing the same thing, well thats a big deal.
They are not migrants, they are illegal invaders.
You repel invaders, not integrate them.
But this will never happen without an uprising of the the people and stop the government that is destroying them on purpose.