At Liberty Law Blog, Mark Pulliam: Jury Nullification: Good or Bad? On the historical background:
Proponents argue that [jury nullification] dates to the refusal of an English jury to convict William Penn for unlawful assembly, a charge that was a transparent pretext for restricting his freedom of religion. Proponents also cite later examples of Americans refusing to convict defendants charged with violating unjust laws such as the Alien and Sedition Act and the Fugitive Slave Act [Ed.: One could also list the neutrality prosecutions of 1793]. …
Some proponents assert that the Founding Fathers contemplated a broad role for juries, entitling them to judge both the facts and the law in any particular case. There is an element of truth to this claim. In the early American republic, the legal system—at least in some states—reflected what legal historian John Phillip Reid calls “a laical jurisprudence” controlled by laymen, not lawyers or judges. During the 19th century, however, virtually all jurisdictions abandoned this practice in favor of the current system of judge-led trials. Accordingly, modern trial practice sharply restricts jurors’ discretion, requiring them to swear under oath that they will follow the courts’ instructions. It is difficult, therefore, now to argue that jurors act nobly by violating that oath and defying the law.
This sounds like a good start to an originalist case for nullification, though I think originalists are divided, and anyway that's not where the essay ends up; from the conclusion:
The debate over jury nullification highlights the differences between libertarians, some of whom are “minarchists” uneasy with the constraints on individual autonomy inherent in the state, and classical liberals, who view civil society as indispensable to secure their liberty. Fundamentally, laws are necessary to preserve a free society, not—as libertarians suppose—inherently symbols of abject coercion. Freedom is not possible without the rule of law. Conceptually, jury nullification—selectively suspending the law—is “anarchy in a microcosm.” As a classical liberal, I view it as brazen lawlessness and a prescription for arbitrariness.
Posted at 6:08 AM