Profiling suspected terrorists can dramatically increase security. Sometimes, it is necessary to curtail civil liberties in order to guarantee national security. Israel, which is often the subject of terrorist attacks, is a good example of how profiling can help security. Suspected terrorists are given extra scrutiny at checkpoints, and this often prevents attacks.
Racial or ethnic profiling of any kind is unacceptable. You cannot stop terrorism by stopping people at airports who fit the description, just as you cannot stop crime in the streets by pulling over suspects who fit the description. It is racism plain and simple, and unacceptable in modern times.