What if someone bombed a mall? What if we have a general description of him? Of course, we get that description out there, so people can pay attention and investigate someone that seems to fit the description. This is a good thing, and completely appropriate in that situation. It's completely different from profiling an ethnic group as being possible terrorists. In this example, if it was merely suspected that the person was, say, purple with yellow spots, that would not be enough to justify detaining and/or investigating anyone who happened to be purple with yellow spots.
With the above example, a crime has been committed, and there is a verified description of the suspect. When profiling potential terrorists, no crime has been committed yet, or there is no verified description. Assuming that it is more likely to have been an Arab and subjecting them to greater scrutiny and suspicion makes that person (and anyone who might look Arab to Joe Security Guard) effectively a suspect of a crime that has not been committed and will likely never be committed by them. As I recall, in this country, you are not a suspect unless there is reasonable cause to suspect you, and you are innocent until proven guilty.
