In the year after Woodstock it seemed rather obvious that Gene Roddenberry was using this episode to tap into the Hippie movement which was sweeping the country after the seminal event of Woodstock. Whatever his motivation, Star Trek prime created a nice story about some young people who are looking to tune in, turn on, and drop out.
They're led by a scientist played by Skip Homeier who has done just that. He also has contracted some kind of biological contagion and as Leonard Nimoy observes, he's quite mad. But Nimoy also kind of connects with Homeier's followers.
Not that they don't have a goal in mind, it's to reach a mythical planet called Eden which is not unlike the Garden Of Eden featured in our Abrahamic monotheist religions.
The rub here is that they reach Eden, but the Creator/Deity has put something in the life on Eden that will truly take care of the infestation of civilization as Homeier and several followers find out to their regret.
An interesting and timely episode taking advantage of a trend in our culture.