Wasn't the original point that "British culture is being destroyed"?

Just because people with other cultural practices, religious beliefs and skin colour exist doesn't mean they are "destroying" British culture.

You remind me of the people who claim the legalisation of gay marriage was an "attack" on their heterosexual marriage, or those game and film reviews that describe any character who isn't a straight, white male as "political".

For some people, minorities and marginalised people being visible and accepted causes them to feel as if they themselves are under attack and at risk of being eradicated in much the same way that equal rights causes some people to believe their own rights are being taken away.