The difference between NDAs and religious esotericism is a matter of cultural respect - NDAs don't offend something people take personally. We could ask a parallel question of whether we should allow posting of pictures that denigrate the Buddha. I would say if any material were found offensive to practitioners of Buddhism, we would be obligated to remove it, no?
In some ways religious esotericism is similarly about respect. I know that there are some few teachings in my tradition (mostly technical details about intensive meditation courses) that we try to keep from new meditators so they don't misunderstand what they aren't ready to hear. If such teachings became public knowledge on the Internet, I'd want to request their removal, because I would feel it would hurt peoples ability to practice my tradition sincerely. I'm sure other teachers feel similarly.
That being said, the Internet doesn't really lend itself well to secrecy; so the question, I think, is whether we feel obligated as a community to respect Buddhism, or whether we are just here to study it impartially.
My feeling is that, since SE does have policies on disrespect, we should at least consider that it might be disrespectful to post teachings that are intended by teachers to be kept secret.
I suppose another difference between NDAs and esoteric teachings is that NDAs deal with a desire to possess something exclusively, whereas esoteric teachings are for the purpose of preventing abuse; they're not really as parallel as they seem at first blush. Esoteric teachings are more like intellectual property, in the sense that the teacher may be seen to have some right to control how they are spread.
td;lr: I'm of the opinion that, out of respect for individual teachers, we consider a policy of responding to requests to take down esoteric teachings by those who consider them esoteric.