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).
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?