The George's Cross is slap bang in the middle of the Union Jack, and was a symbol of the National Front and later the EDL. It is also a military symbol, and linked to the crusades (imperialism).A. the st. george is not a symbol of the british empire, was used centuries before and not only by English people
B. when british empire committed said atrocities it wasn't the st. George waving from HM's ships.
C. the ideology that drove colonialism was mistaken but not outright evil, morality is not determined only by consequences but also by intentions. Colonialism was bad, but that we judge in hindsight, Nazism was bad and it was reasonably known at the time so we could have judged it ex ante.
I don't think that the atrocities carried out in the name of colonialism can be normalised in the way you suggest. In fact, it's absurd of you to do so. To say the imperialists were somehow unaware that what they were doing was wrong is disingenuous; sailing somewhere, taking control through force, and killing all opposition is only mistaken?
The Nazis thought they were doing the right thing too. If they'd have won, people would be saying that it was mistaken, but that we shouldn't judge with hindsight. Don't forget that history is the account of the victors in most cases.
But anyway, don't you wish Woolwich would do something embarrassing so that we can laugh at them a bit?