Nothing would be more ill-advised than allowing juries to think they can simply ignore the law and find a defendant not guilty. Juries are instructed that they must follow the instructions as given to them by the judge and any indication of insurrection should be immediately addressed. In this great republic of ours, we delegate the authority to make and enforce laws to our elected representatives and any sign that the general public might not agree with a certain enacted crime should be dealt with as it occurs. No indication should be given during a criminal trial that the law was enacted for the benefit of just those chosen to decide the case; and it makes not a whit of difference if the jury agrees with it or not, they must find the defendant guilty. Anarchy would result if juries were free to find defendants not guilty simply because they had the notion to do it.
Many a defense attorney has wanted to stand in front of a jury in closing argument and argue that the crime for which the defendant is being prosecuted is really stupid and the twelve people deciding the case can find him not guilty whether he did the act or not. I suspect a mistrial would be instantly declared, the attorney either held in contempt or severely reprimanded, and the defendant required to go through the entire process a second time--probably with more compliant defense counsel.
It is an unfortunate fact that a jury trial is the single, only, specific instance of a citizen having a direct say in what the law should or should not be. And I say unfortunate advisedly. No small group of citizens, such as a jury, should be able to nullify the power of either the state or the federal government. In any other form of insurrection, the group would be instantly jailed and charged with some crime or another and be held to account. As a jury, they can do whatever they want and nothing can be done about it. We need to fix this. We need our legislatures to address this issue and enact some sort of crime whereby jurors can be prosecuted if they do not follow jury instructions. If a legislative body takes its valuable time to pass a law, and the multitude of law enforcement agencies extant make the effort to enforce it, we can't have a group of twelve people ignoring it. Too much time, effort, and money has gone into the process.