In response to Mr. Laser Beam
: That raises an interesting question, though: if Vaal and Landru were created by the progenitors of the societies over which they preside, why wouldn't
they be protected under the Prime Directive? Starfleet is forbidden to interfere with the development of alien cultures, full stop. I doubt it specifies what stage of development (other than that of spacefaring and warp capable, at which point they will by necessity be made aware of the very crowded galaxy they inhabit and deal with the influences of other spacefaring, warp capable civilizations) or allows the captain to disregard the directive if he finds the course the civilization has followed repugnant to his classically liberal sensibilities. If those civilizations, in the course of their "natural" development, decided upon stasis as their so-called endpoint it is still the result of their natural development.
And, regardless of our personal take on the matter, it was canonically established that self-preservation was not sufficient cause to violate it.
In response to Maurice
: the episode seemed to suggest that Vaal was powered by the literal food the Stupid Loompas gathered for it. By not letting them feed Vaal, the landing party weakened it enough for the ships phasers to zap it. And yes, I know how stupid that sounds but I also had the misfortune of seeing The Reincarnaton of Peter Proud
and thus won't put anything past Max Ehrlich, who wrote both that and "The Apple."