Any *right* or *duty* to engage in jury nullification arises from a "higher law" analysis, not in the laws of man.
"We recognize, as appellants urge, the undisputed power of the jury to acquit, even if its verdict is contrary to the law as given by the judge, and contrary to the evidence. This is a power that must exist as long as we adhere to the general verdict in criminal cases, for the courts cannot search the minds of the jurors to find the basis upon which they judge. If the jury feels that the law under which the defendant is accused, is unjust, or that exigent circumstances justified the actions of the accused, or for any reason which appeals to their logic of passion, the jury has the power to acquit, and the courts must abide by that decision." (US vs Moylan, 417 F 2d 1002, 1006 (1969).
The "ability" to do it is because we have a "right" to do it. One has the ability to rape a woman. He has no right to do it. The power to nullify and have it beyond the courts power to overturn that decission makes it a right.
The duty, as you say, comes from a higher law.