CHARLIE X deminstrates just what it was that separated STAR TREK from the other \\\"sci-fi\\\" shows on tv at the time. The main thrust of the plot is about how humans react in extraordinary situations. The sf trappings are incidental, rather than fundamental.
Charlie is a kid who\\\'s been raised without proper adult supervision. As such, he has no discipline, he wants whatever he sees and he wants it now. And he has the power to make those things happen. Kirk tries to fill that authority / father figure role, but eventually Charlie rebels.
1966 audiences would have felt comfortable with the familiar story, despite the alien environment. And STAR TREK was able to gain a foothold in the ratings and do what it was best at doing. Using sf to make engaging observations about the world the rest of us live in.