It appears almost to be a complaint that the NP does not give us certainty , instantly and without effort. But the NP is not like the Ten Commandments, to be obeyed without complete understanding and to be applied in any and all circumstances. Yes, there are ambiguous cases upon which reasonable people may disagree. This in no way invalidates the principle in question. Sometimes, descriptions of certain cases or entities is the best we can do.
People are neither infallible nor omniscient.
The effort will never succeed. In a related vein, Mr. Bradford's discussion of money in a non-free society does not demonstrate that the idea of owning property is unsound. His examples simply demonstrate that moral principles must be practiced consistently. In a non-free society, a moral person does the best he can to live morally. I think Mr. Bradford should remember that a person is not morally liable when he cannot make voluntary, uncoerced choices, i.e., one cannot act in an unfree society as one would in a free society.