A very interesting thread... I did a paper on this subject at University relatively recently, so I will return when I have more time to think about my reply.
However two comments spring to mind:
Mick said this: "Nazism was in essence a reformulation of the same impulse and ideology that instructed the British Empire"
Denzel73 said this: "Every Empire is bad. British was, and it resulted in Pakistani-born terrorists, among other things."
I would disagree with both of them rather wholeheartedly! To compare Nazism, an abhorrent system that believed in the superior race, and the extermination of lesser races is fundamentally wrong. The British Empire was the first to outlaw slavery in 1833, for example, when it was far from 'trendy'. As for the Pakistani terrorists, I'm afraid I don't know enough about the subject, but from what little I do know, it is that the terrorism was homegrown, not as a result of the British Empire.
As for the history of the Empire as a whole, it is difficult to judge simply because of its vast size and the timescale it encompassed. Certainly, there were examples of inexcusable actions - the creation of concentration camps in South Africa during the Boer war for example.
However, Britain did act in what it believed to be best. Abolition of slavery, bringing medicine and technology to its colonies. It secured commerce and trade routes, improved education for its colonial subjects and stood up to the largest tyranny of all - the rise of the Third Reich alone when the rest of the world was in its thrall.
It is impossible to prove one way or another, or to cherry pick examples from history to show one side of the argument, and not the other.
I have more to say on this when I have a bit more time!