Colonialism is and was horrible, full stop, and any time or place someone tries to spin it as a positive, you can always find huge unmarked graves of human misery an inch below the dirt that’s been shovelled over them to hide them from view. Niall Ferguson is only the most recent of a bad bunch of apologists. He’s racist, homophobic, incoherent on economics, and of course, he’s a complete hack.
The only left-wing case for empire I’ve ever heard of was Marx’s whole thing in the 1850s about Western imperalism forcing India and China to modernize (while still decrying the violence involved in that process), but that was based on some pretty Orientalist ideas about “Asiatic” backwardness and has been thoroughly abandoned.