This is a fantastic movie. It is certainly worth a second viewing. In terms of a thesis, how about this one.
The movie "Crash" demonstrates that a crashing of worlds may be the only way people can get rid of their prejudices and learn to accept people as people. Your supporting points can be as follows. First, the various characters in the movie did not know each other, but their lives intersected without their intention. This brought about a situation where a decision had to be made. Second, many of the characters learned something of how other people lived and through this experience they learned to grow and mature as people. Third, the movie points forth to the importance of coming out of your comfort zone to be in the lives of other people to become more human.