Imagine if the British government defended the brutal colonisation of India, by going on about how much they’d invested in the railways they used to ship out all the resources they plundered.

There’s no need to imagine. This argument gets made the time . The British unified India, gave it a railway, a public service , etc. They did actually build infrastructure. People have been using this to justify British colonialism in India for over a century. Before that few in the west thought colonialism required justification. The British built these things in order to make wealthy extraction from their colonies as efficient as possible.