The Prime Directive in "For the World Is Hollow ..."
Okay, here is something for you to ponder. We all know that "The Prime Directive" really got in the way of the Captains of Star Trek a lot over the years. In this one, the landing party had to show the people of Yonada that they were from outside of their world and it doesn't really cause them to "meltdown" too much. In fact, when you see Kirk, Spock and McCoy walking around in the "ball", the people just kind of nod their heads like they see aliens everyday.
The conundrum was, was this a violation of "The Prime Directive" to fix their screwed up navigation system and save them and Darren V from destruction. Kirk says, "It's better than letting them and the people of Darren V be destroyed". HOW DOES HE KNOW THAT?? That is the problem with the Prime Directive. The PD was to keep the Federation from interfering with things that would happen if they didn't interfere. If they hadn't been around, Yonada would have crashed into Darren V and kill everyone of them. What if, in the future, after the Enterprise's interference, the people of Yonada were to be the next Klingons? Or Romulans? What if Darren V were to have something happen that would change the course of history because they weren't destroyed.
Another thing is that they have a library that has the total knowledge of the Fabrini that helps to save Dr. McCoy. Of course, because they weren't destroyed, what if some of that knowledge were to be used for a nefarious reason? What if they had a weapon there that were to be used against another world? I am sure they would have had the technology of space travel given to them. They were a little bit on the superstitious side with that Oracle and a Priestess. A lot of room for some big time screw-ups in the future.
I guess they didn't learn anything from "The City On The Edge Of Forever" did they?