With reinforced cockpit doors, air marshals, hopefully good scanning to prevent weapons on airplanes and a general agreement that nobody is going to be allowed to ever hijack a plane again even if they do assault or kill people or scream about having a bomb the pilot is not going to relinquish control of the plane.... having no-fly lists does now seem superfluous and fundamentally the wrong approach to take.
That said, airlines are still private businesses serving the public and if they are given information that you will potentially be disruptive, then it should be within their right to deny you passage on their aircraft for whatever reason as long as that reason isn't discriminatory using constitutionally protected criteria such as race, or political affiliation, or gender or such. In the same way that a restaurant can refuse to serve someone because of their past behavior. The problem now is that that choice is being made for them.
Regardless, the no-fly list is a determination by someone that you have met some criteria to be kept off of planes, so if we are to remain a nation of laws then people need to be able to effectively challenge that in court. And that means confronting your accuser and challenging all the evidence used in that determination. Otherwise, if we are talking about classified information, then what we should be talking about is surveillance that stays in the realm of surveillance.