Cary L. Brown had a post a while ago in another thread that helped explain why the characters are so important:
by Cary L. Brown
ID, Ego, and SuperEgo.
Or, in probably more "easily recognizable" terms... the heart, the mind, and the will.
McCoy was always the heart. Spock was always the mind. And Kirk was always the will. And the three of them, together, were stronger than the sum of their parts.
I don't think this was Roddenberry's original intention... at least, not entirely. But it ended up working out that way, and that's a large part of why classic Trek worked so well. Basically, you had three character who, together, could voice all the internal struggles we all go through. We all have those three sides, and they're often in conflict... but nobody hears what's going on inside of our heads (unless we're the sorts who walk down the sidewalk of San Francisco talking to ourselves!)
The three characters added together equal the human psyche. If we were to have only one protagonist in this film, and we wanted to know how he was dealing with the situation at hand, we would need comic-book thought bubbles or the old cliched "devil and angel on his shoulder". This would be quite silly, so instead we are given the human psyche as three characters -- each free to voice their opinions to the other two.
Many of the best Star Treks used this simplistic -- but clear and easy to understand -- illustration of how a human
psyche will react to a situation.
The "big ideas" and the characters are very important to the story, because without the "ideas" there would be nothing for the three characters (different parts of our psyche) over which to have a conflict, and without that conflict among those characters, the story would be very boring indeed.
When I say "conflict", I'm not saying I want to see a big fight among the three main characters. But in every good Star Trek, there was always a slight -- but respectful -- difference of opinion among those three...just like what happens inside your head when you are presented with a situation that requires a resolution.
That "situation that requires resolution" does not need to be "Plucked from Today's Headlines". It could be one of the classic plotlines that spring from human nature -- Greed, Ambition, Love, Revenge, Survival. The types of stories that Shakespeare wrote, or the ancient Greek playwrights such as Aeschylus, Sophocles and Euripides. Their stories still ring true today, even though their basic plotlines were about human nature.
I don't mind social commentary, but this should be about how we as Humans "deal with" social issues -- this should not be about the social issues themselves.