Can you elaborate? I am unaware of the British Empire dehumanizing British settlers in Rhodesia. You don't have in mind the Boer wars, by any chance? That's a different country (and the Boers were not descendants of Brits, too, speaking a different language, for example).

I still don't see much of dehumanizing. What you have is a fight over political power in the age where the idea that "All men are created equal" wasn't either widespread or popular (outside of the religious context).

Basically, you need to show that the metropoles treat the colonists much worse than comparable groups in the metropolis itself. For example, if you have an uprising in the colony, it was suppressed much more harshly than, say, a similar uprising in the metropolis.

Your example of Spanish colonies seems to speak to racism much more than to the metropolis dehumanizing its own colonists.

How many nukes do you think is enough? Will 1 million be? Modern USA can build that in few years if they want so. Do you think colony (with some future technology) will definitely be unable?

How did you get that idea? Quick search for the cost of a single bomb is $20 million. That means you are looking at a cost of 20 trillion$. Given that the amount of cheaply minable uranium isn't infinitive the cost is likely more.

How one treats the workers in the space industry doesn't even really come into the worry I'm entertaining. The most plausible way to get an Earth-space war isn't the staff of a space telescope suddenly discovering a yen for nation-founding - That's just so unlikely I can't be bothered to work out how unlikely it actually is.

The only semi-plausible way to get there is for a couple of very specific groups to go into space colonization specifically because they have mythologized both the american independence war, and space as a conveniently natives-free analogy of the american west - IE, radicals with a hardon for revolution, and the impression a height advantage will make it more feasible. I'm not worried about people getting radicalized in space, but about existing radicals concentrating there. Which is still pretty bloody unlikely, but tbh, if I was hiring miners for the belt, I'd be .. rather reluctant to hire people with radical political views. It only takes one person who has read too much Heinlein to deliberately set off a collision cascade in LEO*, and there comes bankruptcy. Also the inevitable death of everyone on the high side of the shit-storm when it turns out self-sufficiency is much harder than it looks, but that doesn't clean up the mess.

*I have no idea why the "American Revolution 2.0" books never use this as a weapon, but instead insist on killing massive numbers of people on earth. Blocking access between space and earth for a couple of decades is bloody well trivial if that is really what you want to do - Grind an asteroid into sand, put the sand into the right orbits, and now going up and down is suddenly very, very unsafe until it deorbits. Very hard to undo, but.. if you are dropping rocks on earth, that comes with even /less/ options for changing your mind later.