Unfortunately, while not false (in the most obvious case, informants have a way of winding up dead if you are too obvious about their existence); your justification leaves two major issues unaddressed:
1. The government is not refusing to divulge the specific reasons and evidence that led to a particular person being added to the list(which quite plausibly might reveal specific informants, bugged computers, etc. and would likely merit an in camera review or something). They are refusing to divulge the general criteria and possible methods by which anyone could end up on the list. It's the difference between "Tell me exactly who ratted out Big Vinnie" and "What constitutes 'Racketeering' for the purposes of the US criminal code". One is a potential operational risk. The other is 'rule of law'.
2. The 'no fly list' is a bullshit twilight category without obvious protective value. Apparently there are people (and lots of them) so dangerous that they cannot be allowed on a passenger aircraft, even with some sort of enhanced screening; but so safe that apparently no other measures need be taken. It's a combination of state harassment(not being able to fly is a pretty big deal if you travel much) and absurd magical thinking. Too dangerous to fly; but safe enough to do basically anything else? Seriously? Why would that category even exist? Hijacking an airplane with a pointy object shouldn't work anymore(if we finished upgrading the doors), and anyone who can get bombs, firearms, or toxins doesn't need a plane to cause trouble.
The refusal to even outline how you fall into such a category, or why such a category exists, is a profound mockery of the notion of rule of law. No, not every specific detail of how every piece of evidence is gathered can be safely revealed; but that isn't the story here.