Jury nullification is typically portrayed as a defense against unjust laws, and some judicial thinkers see it that way.
But it's important to point out the dominant view and the current view of jurisprudence views jury nullification as kind of an unfortunate edge case. Here's the Fourth Circuit from 1969:
"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 or passion, the jury has the power to acquit, and the courts must abide by that decision."
In other words, jury nullification is not a defense against injustice, but a side effect of having trials by an independent jury of ordinary citizens.
In the opinion of a court, which would rather not recognize the concept at all. Courts hold a dim opinion of jury nullification, going so far as to legally sanction mentions of it in a courtroom, and to provide "instructions" to the jury that try to expressly prohibit them from considering anything other than whether the facts of the case meet the law as explained to them. Even hinting that you might understand the concept will get you thrown off a jury. In some cases, bringing up the concept during jury deliberations will result in a mistrial.
Personally, I like the way the state of Oregon handles the issue. Quoting the Oregon constitution, article I, section 16: "In all criminal cases whatever, the jury shall have the right to determine the law, and the facts under the direction of the Court as to the law, and the right of new trial". That said, I don't know whether in practice Oregon courts do any better about not censuring jury nullification.
It's a mistrial because you're telling the judge he's not important. Of course judges don't like that, they worked their whole life to be a judge, and some jamoke without a law degree shows up talking about jury nullification. That's why you see censures and mistrials.
Clearly, the Fourth Circuit at the time saw it that way. But that does not address the question of how was it viewed by the Framers who gaurunteed one (at least on the Federal level) in Article III. It also does not address the question (perhaps more relevant today) of what ought it to be and how ought it be treated?
It is possible, indeed likely given the history, that the Framer's saw providing nullifcation as part of the purpose of enshrining a jury trial in the Constitution.
Whether they saw it that way or not, the relevant question is, how ought we treat it? Should we treat it as an unfortunate side effect that we can't completely get rid of but should do everything we can to minimize? Or something to be embraced as essential? Or perhaps in between those two extremes, as something genuinely useful, but only "in extremis" when all better options have failed?
Well, original intent as a theory of law interpretation is considered problematic, and not really used by anyone. You can't necessarily read lawmakers' minds, and lots of law--especially the Constitution--was written by many different personalities often at odds with each other, where 'original intent' might not exist even theoretically.
Some people confuse the 'original meaning' theories of someone like Scalia with original intent, particularly since the words of the Founders could be used to support either theory. But it's a different thing. So you can talk about what the Founders meant, and it's a fine thing to think about, but it's not something that will get you far in the courtroom unless you can link that to what is written and what is in common law.
I should disclaim that I am not a lawyer, but there are legal scholars that discuss actually using original intent and courts that cite specifically to intent in their decisions. Though, I agree fully that in attempting to argue intent you must still be able to tie it to what is written.
I also fully concur that many laws may mean different things even to the people involved in passing them, yet some times they can be clear, especially when laid out in clear records of the debate or in an explicit intent section as part of the bill.
The intent, when known, can help inform the way a law will be interpreted by the courts. Prof. Ian Bartrum discusses this in "The Modalities of Constitutional Argument" and Prof. Philip Bobbit goes into more detail in "Constitutional Fate" and "Constitutional Interpretation."
You have a good point that Scalia's 'Original meaning' is different from 'Original intent' and 'Original meaning' is far more objective. But that does not mean intent is not considered. For a modern case where Congressional intent was at the center of an 11th Circ. decision look at Harris v. H&W contracting Company, 102 F. 3d 516 (11th Circ, 1996).
[Edited to remove a redundancy]
Thouh, while I think intent here has relevance, I still think the more salient question is prudential. Regardless of how it came to exist, what should the role of jury nullification be?
The very first thing that wikipedia says about jury nullification paints it as much more than "an unfortunate edge case":
A jury verdict contrary to the letter of the law pertains only to the particular case before it; however, if a pattern of acquittals develops [...] it can have the de facto effect of invalidating the statute. A pattern of jury nullification may indicate public opposition to an unwanted legislative enactment.
Wikipedia and cynicalkane aren't conflicting. cynicalkane is making a claim about why nullification exists. (It is impossible to prohibit nullification without also giving courts the power to ignore jury decisions based on what they think is in the jurors' heads.) Wikipedia is making a claim about the effect of nullification. (Nullification can effectively repeal laws, a very powerful consequence.)
But it's important to point out the dominant view and the current view of jurisprudence views jury nullification as kind of an unfortunate edge case. Here's the Fourth Circuit from 1969:
"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 or passion, the jury has the power to acquit, and the courts must abide by that decision."
In other words, jury nullification is not a defense against injustice, but a side effect of having trials by an independent jury of ordinary citizens.