First, although we can block those on the terrorist watch list from getting on airplanes, suspected terrorist activity is not itself a sufficient reason under current law to prevent them from buying guns from licensed dealers (the "terror gap"). Second, even if we could block suspected terrorists (and other violent people) from buying guns from licensed dealers, they could evade Brady Law background checks entirely by resorting to private sellers at gun shows (the "gun show loophole").My problem here is the totally casual way we trample the entire concept of due process. If the people on the no fly list have committed a crime, charge them, arrest them and prosecute them in a court of law. The whole concept of a secret government list which no one know how they got on or how they can get off, no one is allowed to face or even question their "attackers," in fact, no one can even find out whether they're on the list or not is anathema to the principals this country was founded on.
The guarantees of the Constitution and the Bill of Rights were, in fact, designed to protect citizens of the United States against exactly this sort of Star Chamber prosecution.