"Freedom at last!" says Kimus. Because he's flying in an air car.
"You're not free yet," the Doctor reminds him.
Kimus observes that he's "free to think", yet doesn't seem to be doing so.
They chat about how Kimus' world works. It has mines that function by themselves.
"What happens when they run out?" asks the Doctor.
"The Captain announces a new Golden Age of Prosperity and they just fill up again."
Kimus notices a certain reserve in the Doctor's manner.
"You don't think that's... well... wrong? Do you?"
"It's an economic miracle," says the Doctor, "of course it's wrong."
What actually happens, of course, is planetary piracy. Or, to give it another name, imperialism. Kimus' planet ("Zanak" as Romana or Mula would helpfully remind us) materialises around other planets and then mines them down to a tiny, crushed pulp, killing anyone who happens to live on them in the process.
Real imperialism is considerably more complex than this... but the basic picture is essentially right.
Much as the people might stagily cry "hooray!" for the Captain whenever he announces another Golden Age of Prosperity, they are not the ones he serves. Their tyranny is one which gives them fine clothes and jewels to kick around the street, but that's a by-product. The crushed planets are fed into a system to keep an ancient queen alive. Stuck forever at a moment of near-deathly stasis, her need for energy is nevertheless immense... and growing. The energy flows in from the crushed planets to the ravenous centre of the system. And the hunger at the centre only grows. The more it gets, the more it needs. The real dividends always fall. The crisis looms, and the only way to fend it off is to extend further and further, to accumulate more and more and more. And with every extension, the hunger grows.