In response, you're goddamned right they can be denied a privilege. Do you think a repeat-offender drunk driver who has killed should have the privilege to drive again? Not a chance.
Now, if you want to argue that they were denied the privilege to fly without due process, well, there's no due process for preemptively denying that privilege. The guy's name showed on a watch list - there's usually a reason for it and for those who shouldn't be there, they have legal recourse to get removed.
Your arguments are red herrings laden with a smattering of pure bullshit. This guy has a right to walk anywhere he wants, travel freely, until someone with more power gets in his way. Sucks to be him.