More dynamism, people could give better ideas and less corruption than in more authoritarian countries. In authoritarian countries, everyone is relying on one person. What if that person is incompetent or dies?
I just want to point out that imperialism is not exclusive to democracy. There are absolute monarchies and dictatorships that are imperialistic. Maybe your criticism of democracy as being imperialistic is more about capitalism and drive for exploitation and profit, not at democracy?