"Bad things" are done during times of war .. And no country is exempt from blame of doing bad things .. The Nazis performed unspeakable and unparrallelled 'bad things', on such a large scale ... And that is why they stand out head and shoulders above the rest.
If you are talking about WWII, it is because the Allies won, and the Germans lost. The good guys always win wars, because they are the ones who write the history books! :)
The British did a lot of dreadful things in the pursuit of Empire, it's true.
Of course, they did not necessarily realize what they were doing was bad.
The "Empire Builders" from Clive to Rhodes truly (and fancifully) believed that they were bringing "civilisation" to undeveloped countries.
As for looting countries of their treasures, yes, we did that too - London's museums and England's stately homes are testament to that.
We were also along with others, deeply involved in the slave trade, but that has already been much discussed in here, and I have nothing to add.
But we did, for the most part, leave countries in a more prosperous state than we found them (although not necessarily more politically stable), and travelling and working all over the world as I have, it seems that the "end of Empire" is (generally-speaking) regarded with more than a little nostalgia by those who are most "rich in years".
So far as I have been able to make out, we never indulged in mass genocide, and "dislike of the unlike" has never been a particularly British trait.
It just isn't on the level of the Holocaust. There has never been anything of that scope before or since.
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