I can understand why people consider this episode preachy. And in some sense, I think that's a wonderful thing. Not wonderful that the episode is preachy, wonderful that people *think* so.
Because if people think it is preachy, it means that its message is obvious. But it's a message that has frequently NOT been obvious to people, in many times and places in human history. The theme of the individual versus the state is an absolutely timeless one, and the message is one that needs to be told again and again in every generation.
And the story *is* told timelessly. As much as one is tempted to see it from the cold-war context of its time as being a thinly-veiled anti-communism fable, the truth is that The State as presented here is any tyrannical totalitarian regime, be it Marxist, Nazi, or any other statist ideology.
The one flaw, for which I took off a star, is the invocation of religion. Religion is an ideological detail, not a fundamental to the theme. The State's outlawing of religion in this tale serves as too-concrete a connection with the Soviet Union of the era. It also excludes The State from potentially representing any kind of theocratic totalitarianism (which is just as bad).
But it's such a good episode, and the message so important, that I'm willing to cut it a lot of slack for that flaw.