It's also why I think William Dalrymple's line that "the British empire was built on skulls" is pretty unhelpful. History is built on skulls. The British Empire was not notably more bloodthirsty than any other empire in history - including empires that aren't thought of as such. Germany was an empire in itself in the 19th century - the Prussian conquest of central Europe. France was an empire in itself in the 10th century. When will President Hollande apologise to the people of the Humber for the Harrowing of the North? Should David Cameron return the favour by apologising for the slaughter of prisoners at Agincourt? Does this really get us anywhere?
As to Amritsar itself, it's an issue that has received its fair share of academic attention. It's not, however, an entirely unambiguous example of British cruelty and bloodlust. A controversial revisionist view of it is set out here, with the take-away for me being that Amritsar ought to be seen in the context of a widespread national insurrection, and the total breakdown of order in Amritsar itself. On this reading, Dyer's behaviour after the massacre looks almost more blameworthy than his behaviour leading up to it.