I hate that we live under a mental paradigm that the only thing that matters is efficiency, ad infinitum and ad nauseam.

Take one more step, and you've got it. Efficiency only matters because it maximizes PROFIT, and Profit is all that matters. We are Ferengi, at our core.

So the reason to do it is because uncontrolled, unregulated profit-gouging has made the Earth literally unliveable. We haven't reached that point yet, but we are certainly on that path, and those who would protect us from the inevitable outcome, won't even acknowledge that the problem exists, calling it a hoax, and even forcing their alternative hoax to be governmental dogma.

It seems like those who control the money have already decided that this is our future, so it's perfectly acceptable to destroy this environment, in order to create enough profit to build the next environment, which will be reserved for the Sociopathic Oligarchs.

Also, it could travel to find distant worlds to colonise

(It'd have to accelerate slooooowly though)

Maybe... or would your body simply rot away faster since you aren't using it as much? I would be inclined to think the latter.

This is my assumption about what's likely to occur as well. And a song about it: King Gizzard and the Lizard Wizard - Mars for the Rich

Great, that covers the first generation in charge. What are the long term educational, economic, political, social, and cultural institutions that will keep things going when everyone alive will have been born on the ship/station, and nobody has first hand knowledge of how it started?