Except for when human law goes against natural law.
Against whose idea of natural law?
Yours and mine are probably very similar (if not identical), but that is not so for everyone.
And, if people turn away from the laws and courts which they themselves have established — then there is no mediator or mechanism for resolving conflicts between each individual’s concept of natural law.
Which isn’t to say that such conflict can not be resolved — it just can not be resolved without resort to the law of the jungle and force of arms.