These people haven't been to London, have they? It's one of the worlds major multi-ethnic cities (and quite a surprise to people who thought they were going somewhere which fitted their preconceptions of "English").
with some bits :empire: omitted in the interest of tact and not dividing things, probably rightly so
Those empire bits made London the multi-ethnic city that it is. Without being the capital of a globe spanning empire, all of those people would not have spoken English. An unwillingness to appreciate that English/Anglo-Saxons, Scots/Picts, and Welsh/Celts went out and subjugated 1/5 the world's population (1922) means turning a blind eye to the particular reality that makes London what it is.
Well, I certainly appreciate your point, but if the ceremony had invoked the Empire, then that means opening a whole other bag of political dogs which simply do not belong in an international event like the Olympics. Emphasis on the International part, here.
Historians, particularly British ones, make careers from arguing the toss on wether the Empire benefitted or hindered the world. Quite simply, the answer is murky as the River Thames.
Yes, the infrastructue was beneficial, yes, it had some hand in spreading democratic ideals and yes it layed the foundations of the modern world.
BUT, that also comes with some significant baggage, inc. but not ltd to, involvement in the slave trade, surpression of native populations, human rights abuses, economic pillaging of nations under the flag and some responsibilty for the shambles of some former colonies today.
Croke Park in Ireland, The Sepoy Mutiny in India, Mau Mau rebels in Kenya, The Opium wars in China, the Second Anglo-Boer War, things like these are part and parcel of Britian's "Imperial" past which you simply cannot omit when bringing it up.
In short, the point is that in an Olympic Opening Ceremony you want to showcase the best of the Nation. You simply cannot show the best of the Empire without showing the worst, it is impossible. On top of that, it would be thoroughly insulting to many of the Nations taking part in the Games to see Redcoats paraded across the stadium, metaphorically or literally.
It would be simmilar the USA celebrtaing its own diversity by doing a musical homage to the slave trade. Just plain wrong.