It is not a good idea to regulate all the time when in fact every regulation could effectively be a wall.
The article treats this principle basically as ambiguous.
So this principle could be not perfectly defined for some, or disputable, according to the article.
However, you miss the point.
Saying that this principle is just not strictly defined (according to the article) does not make it a reason to put it to the trash directly. You have to compare to the status quo.
For me what the article supports (implicitly) behind this reasoning would be that the status quo (coaction and violence by governors) is better: hey, just proceed with coaction because NAP is not perfect? I think there is a lot of consensus on things that are wrong that we would all accept. Consider it a subset of NAP. The bigger the subset, the better for everyone.
In fact, there is a very clear principle, at least in my opinion that can define things way less ambiguously: it exists the negative or natural law and positive law.
For me, basically, negative rights should be inviolable and positive rights are not rights as themselves in my opinion: none of us will ever have infinite capacity or power for an arbitrary action, and in doing so you will violate the negative rights of others: I want to date this girl (but she does not), I want to go to Harvard (but I need to spoil others and disregard their academic CVs and skip the line), I want to have 10000 usd per month (but my employer built the business and won't pay that)... no, those are not rights. Those are things we earn by ourselves or figure out how to do.
Vaccines.. at what level of disease severity should the government forcibly inject the entire populace with a vaccine to ensure that no one can aggress on another by infecting them (on purpose or accidentally).
If one jumbo jet passenger has a severe peanut allergy and other opens a bag of peanuts, is it an act of aggression?
