Just because they are also Arabic does not mean they are "some of their brethren"! I'm Irish, too, but I didn't get searched going into London because I might have "brethren" among the IRA. Some of my Arabic friends who have been harassed are generations removed from these "brethren" and have no ties to the Middle East at all, but "patriots" use this idea as an excuse to abuse them. We nearly had to call the police because a man started screaming at my Jordanian-American coworker--whom he didn't even know was Arabic until he saw his name tag--and we were literally afraid the man was going to punch him.

There's a "calculated risk" that the guy next to you on the plane might be a tweaker or a schizophrenic or a disgruntled postal employee, too, but I don't think they profile for any of those.