The Doctor gets huffy and righteous about this, escapes the city and comes into contact with a "savage" who had previously been sucked nearly-dry in the laboratory. He arranges for medicine to help the man but is recaptured by soldiers from the city. Thus ensues a two pronged effort to undo the situation between these two peoples. The Doctor has in previous episodes sworn to not meddle and not interfere with the course of history, but in this case he chooses to destroy the 'evil' of sucking life force from unwilling victims. It strikes me as a bit of inconsistency, in some instances he does not interfere but in instances like this he does interfere.
Interestingly at one point he equates this life-force-stealing practice as akin to the Daleks. That is surely the source of his stand to destroy the evil practice. And surely it is a rather bad thing to be stealing life force from people like this.
A curious sequence occurs when the Doctor's life force is taken after his recapture. This is treated as a special event and that the laboratory had never been used to take life force from a highly advanced being such as the Doctor. As an experiment the leader of the city, Jano, insisted that he be given the energy stolen from the Doctor. Immediately after the "intransference" Jano takes on mannerisms and memories from the Doctor and over time makes attempts to destroy the machines and finally Jano joins the "savages". Together they plot to destroy the machines because the Doctor points out how Jano now has learned the difference between Right and Wrong. Hurm, how could a highly advanced civilization not have a sense of Wrong/Right? But for that matter how can an highly advanced civilization do as they were doing?
That last question has an odd answer for me ... To my eye this arrangement is very similar to the treatment of workerbees by corporations. Workers are treated as disposable parts not as people. Workers life is taken one day at a time. Workers do not get to choose their work, they are told what to do and when, and disobeyment results in firing. The analogy isn't quite perfect to the portrayal in the story but not far.
I tend to think the question being studied in this story is individual freedom.