 Which is not a reason the captain does not want to create a police force?
The decision of Interstellar was that the colonists started a revolution far out in space, that it was fanned by the ignorance of Captain Sessions in dealing with such matters. It ended with passengers engaging in open warfare with each other and the crew. We don't think anything is going to happen, but if it does, we want to get an impersonal, unprejudiced view. Basically, it was an instrument which would open distant vistas to colonization, reducing the shoulder-to-shoulder pressure of a crowded solar system. He said it was significant that all en route had passed stability tests, and that it was to the ship's discredit that someone with criminal tendencies should have been permitted aboard.
 He figures passengers will eventually be blamed
 He doesn't want to violate the trust of the crew  He does not have people to spare  He doesn't think it's part of his job  He figures passengers will eventually be blamed