This is not because you understand the theory of evolution that you consider it a moral thing to happen.

Actually, letting the weak die and selecting only the fittest is almost diametrically opposed to the very idea of civilization. Our goal as civilized animals is to make selection an outdated part of evolution. Cure the sick, help the handicap, preserve the old, protect the young.

We don't let people die to diseases in order to strengthen mankind. We take the helm and exterminate pathogens.

Imperialism has both good and bad. The bad comes in the form of top down governance. The good comes in the form of modernization. See Roman and imperial China Empires among others.

True. If you want modernisation from imperialism then you get top down governance. You can't have your cake and eat it too.

Umm that is exactly what happens with colonization - the colony grows big enough to be self-sufficient and starts getting its potential squandered by the home country's top down governce seeing them as a resource reserve instead of another part of their country.

Either things are reorganized such that they gain more local autonomy granted effectively losing the top down control or they break off. In either case they typically do better because of it. Even with problems in the aftermath they typically rise further - India for instance.