Because when it comes down to it... we pretty much run the country - monarch/house of commons/house of lords, run most major businesses, make up the majority of public and private school students and generally aren't a minority in any shape or form.
Awaiting a neg for this frankly, but it's the truth
EDIT:
Just in a response to the negs I suppose... I was not implying that I support the above status quo, merely that exists, and for me is why I feel that anti white racism is seen as more acceptable, our culture has downtrodden ethnic minorities for hundreds of years.