It is useless to debate the original sins of colonialism, particularly since I don't consider it to have been "bad" in any current sense. It was simply what the more dynamic societies were capable of doing and might profit from during the age of exploration. Of course, once a colony is established getting rid of it becomes a whole 'nother problem.
What we should learn from is the global rush to end colonialism that left us with the tyrants and splintered societies that represent africa, parts of Asia, and the middle east today.
Deep in the hearts of western liberals I think we even worked to defeat potential good guys simply because they might have been linked with previous colonial powers [Ho, Nasser, Castro, Mandela, all had support within western elites.]