When did you become the official judge of who is a terrorist? What happens when you're walking to the store one day, a protest passes by, and you no longer can fly ever again because you were identified on camera in a protest? "But I was just talking to the store!" Sorry, you cannot defend yourself against this because there no longer is any due process. You were on camera and that's the entire process. That part of your life that involves flying is now over regardless of your (non-existent) level of involvement in the protest.
You really should be careful what you wish for because at this rate, you're probably going to get it and much more of it than you ever imagined.
Edit: the no-fly list as a DHS entity, which I just learned about, is absolute horseshit. I assumed no-fly lists were per airline and I stand corrected.
Terrorism is an over-applied label that is used to stoke FUD and expand executive power; yep I agree with that and I don’t use the term lightly.
Joining an organized movement to overturn a legal democratic election, breaking into the capitol, armed, and bludgeoning an officer to death is terrorism and a private company has every right to deny these people the privilege of flying on their airlines.
The no-fly list is an important element of suppressing terrorism, foreign and domestic. It exists to prevent precisely this sort of situation - very few of these people were from within driving distance of Washington (or each other).
Whether it could do with more oversight is an independent question, with no shortage of people to ask it.
You really should be careful what you wish for because at this rate, you're probably going to get it and much more of it than you ever imagined.