Star Trek: The Original Series, Season 3

Kirk:
They really believe that (the planet) Eden exists?

Spock:
Many myths are based on truth, Captain. And they are not unintelligent. Their leader, Dr. Sevrin, is a man --

Kirk:
[surprised] Dr. Sevrin is their leader?

Spock:
Yes. A brilliant research engineer in the fields of acoustics, communications and electronics on Tiberon. He was dismissed from his post when he started this movement. Tong Rad inherits his father's extraordinary abilities in the field of space studies.

Kirk:
But... they've rejected all that, and all that this technology provides. And they seek the primitive.

Spock:
There are many who are... uncomfortable with what we have created. It is almost a biological rebellion. A profound revulsion against the planned communities. The programming. The sterilized, artfully balanced atmospheres. They hunger for an Eden... where spring comes.

Kirk:
We all do. The cave is deep in our memory.

Spock:
Yes, that is true, Captain.

Kirk:
But we don't steal space cruisers and act like irresponsible children. What makes you so sympathetic toward them?

Spock:
It is not "sympathy" so much as curiosity, Captain. A wish to understand. They regard themselves as aliens in their own worlds. A condition with which I am somewhat familiar.