My emphasis on the second phrase. Roddenberry really did seem to conceive Trek, early on, as a way of doing a show like "The Twilight Zone" in a more practical way.
Space travel was key to the format less because he was interested in space exploration or the future per se than because he was seeking a format in which the continuing characters could encounter just about any conceivable situation or setting, at any period of history.
This somewhat naive notion that the "infinite universe" made anything and everything plausible served that end.
Unprecedentedly, I agree with every word in Dennis's post.
Save one.