Mulan,
The government has a 'bad guys' list and you would be surprised to see the kinds of names that are on it. You cannot just screen Muslim looking people. You have to remember that there are the muslims that appear arab/iranian and then are black muslims with an axe to grind (the Black Panthers were/are a very violent group). Then you have the IRA .............full of white Irish people from all age groups. You have Mafia organizations, Columbian terrorists who kidnap people, you have the Mexican Mafia and as we saw on tv, there are Basque groups that will be violent.
You never know just who is a terrorist these days. Besides, if they skip you to frisk the Arab sheik behind you and he is not a terrorist they can start suing the ACLU for profiling.