Crash was a good film if all the characters were the same color. Since there's no racists in thing movie.
The fears the character have is just from fearing a sub-group of people that they don't interact with regularly (and it also finds the 10 most segregated people in LA). The problem is that real racist genuinely believe that they are being smart and well-informed by believing that another group of people is inferior so that is a hell of a lot more complex of an issue than what this movie is about.
That's the reason a lot of people say that this movie doesn't have any subtlety. It doesn't have any real message but it tries to claim that it's about racism.