Feeling secure in my credentials as a progressive, far-out on the political left all my life, a social-justice warrior and anti-war demonstrator as far back as 1968, I’m going to say something that my allies on the left must react against: in 2019, colonialism likely would not be worse for many parts of the world where the British or French once ruled. The regimes in post-colonial lands now are so often atrociously bad.
Had Europeans stayed at peace in Europe, with no great wars in 1914 and 1939, their empires might have evolved, been liberalized by domestic democratic forces back home in European nations, and the development of the colonial lands might have been less deformed than what has happened in the 20th century.
Hong Kong would be fortunate to have British rule still, Pakistan, Egypt, and India perhaps. Many parts of West Africa would be better off if French rule lasted.
The man who argues this most forcefully in English is Niall Ferguson, if you care to research the topic.
Natives of North America are not included in my alternative-history vision, however, since for them being settled by Europeans has been so demonstrably genocidal.
Had empires of Europe never found the western hemisphere, the path of development here could have unfolded in ways no one can imagine. It would not be utopia, but it would be unique and very unlikely to be worse for natives.
Counterfactual history is entertaining, but insubstantial. No one can know the result of a hypothetical. But people of strong views opposed to colonialism act as if they know that colonial rule was never capable of good effects, and that is false.
“The best lack all conviction, the worst are filled with a passionate intensity.” True of our politics now, as when Yeats wrote these words 100 years ago.