> How the British and other colonizers go unpunished

And who would do that punishment? Colonization occurred because country X had overwhelming military strength over country Y, defeats it militarily and then occupied it. Absolutely nothing new historically or humanly wise: it's like this since the dawn of time; and it's true in the animal world too. The only way for Sri Lanka to "punish" England is to become military strong but whining on a website (created by a descendant country of the said colonizer) won't do it. And if anything most of the former colonial powers, to the notable exception of Japan, are currently willingly punishing themselves already by allowing millions of people from former colonies to immigrate.