And yes, obviously a bunch of people working together in the same profession are going to have some similarities; you're not likely to see someone who doesn't
want to explore the galaxy aboard a starship whose mission is to explore the galaxy. QUOTE]
You're showing a lack of imagination.
You could have a real diversity of reasons for serving in Starfleet aboard a starship.
1) Character from a planet attacked by unknown aliens who is dedicated to tracking them down and avenging his family.
2) Character who has religious beliefs that believes if they go far enough across the galaxy that they can "touch the face of God".
3) Character running away from trouble on their own planet (French Foreign Legion motivation).
And so on.
And "chocolate, Westerns".
Those are quirks. Not personality.