The following is a list of possible value / criterion pairs for the jury nullification resolution.
A couple questions to kickstart your thinking: Why would we have checks on government? Why do we have jury trials, anyway? Why not just have judges decide innocence or guilt?
A work in progress. Suggest your own pairs in the comments!
C: Governmental Legitimacy / the Social Contract
If nullification is a "just check" on government power, it's because of the nature of government's relation to its citizens. A government that oversteps its bounds with unjust laws--even those that are initiated through democratic processes--has violated the social contract. Nullification, then, is a peaceful form of revolution. (You might compare these V/C pairs to those I wrote up for the vigilantism resolution a year ago.)
C: Popular Sovereignty
At its core, the U.S. strives to be democratic. Popular sovereignty--the idea that the people rule--is the foundation of democracy. Jury nullification places power in the hands of the people, the power to declare that the law is unjust, and that the government has overreached. Combine with arguments that institutions have been corrupted or have stagnated (undue corporate influence, special interest groups, etc.) and you can be the Noam Chomsky of jury nullification.
V: Individual Rights
C: Reducing state power
Similar to the argument above: we live in an age of ever-expanding state power. The justice system in the United States is a well-oiled machine, grinding individuals to powder. Nullification jams the gears, protecting individual rights--especially of those who are unable to afford the best attorneys. (The War on Drugs makes this problem acute; see Paul Butler's Let's Get Free. for a former prosecutor's take on the practice.)
V: Justice / Democracy
C: The Rule of Law / Due Process of Law
It takes only one nullifier to hang a jury trial. This has the potential to jam the gears of justice, which is one of the primary reasons juries are never instructed about the power of nullification. Furthermore, it's patently unfair and undemocratic for one person to thwart societal standards.
Because of a little process called "voir dire," a potential nullifier is likely to have to lie--after all, no prosecutor is going to let a person who reviles the drug war stay on a jury in a drug case. But deontological ethics--especially Kant's--forbid lying, even for the sake of the good. (Here it helps to define "justice" as "moral rightness.")
V: The Rule of Law
C: Respecting legal expertise
Ordinary citizens, God bless 'em, don't understand the complexities of the law, questions of constitutionality, and the like. Although the United States has democratic aspects, it is ultimately a constitutional republic, which resists the fickle fervor of the masses. Leave legislation and judicial review to those who are not only appointed, but qualified to do them.
Going Either Way
In the United States, the Constitution, as the supreme law of the land, is the ultimate standard of justice. Is jury nullification constitutional? There's no right to it--the practice comes from common law--but it's not clearly unconstitutional, either. Essentially, the Supreme Court's few rulings on the subject say that it's a power juries have, but that jurors have no right to be told about it.
V: Societal Welfare
C: Consequentialism / Utilitarianism
If we should evaluate governmental actions--and checks on government power--in the light of their societal consequences, is jury nullification justified?