The question is one of authority. Where does the Constitution give you the authority to declare a law to be "unlawful"?
Allow me to illustrate: In professional sports events, such as basketball, there are specific officials who have been given authority to declare a move illegal for one reason or another. A referee may declare a foul, double-dribble, traveling, etc.
The actual RULES are written and everyone knows them. There's no question about those.
But who has the AUTHORITY to call fouls? Who has the whistle? Who wears the black and white stripes?
By contrast, would it be OK for one of the players to bring a whistle and call fouls (or other violations) while playing? No. And it's not because a rule is right or wrong, or a question of whether or not a violation occurred. Neither of those issues matters, because a player simply doesn't have that authority.
It's my contention that a juror does not--and SHOULD not--have the authority to interpret the law and declare one to be "unlawful" or un-Constitutional. That authority is EXPLICITLY and SPECIFICALLY granted to the courts, up to the Supreme Court.
A juror is not granted that authority when sworn in as an active juror. He is not given that authority by the Constitution. If we are to accept that a citizen can take upon himself authority as he sees fit, as long as he's really sure he's right, then our nation will be utter chaos in no time.
Further, imagine that a home plate umpire were to call every pitch "thrown" by X's pitcher a strike, even if it rolled across the plate, and call every pitch thrown by Y's pitcher a ball, even if it passed perfectly through the strike zone. Team Y bats first, and gets retired by nine consecutive pitches, all of which roll across the plate but are called strikes. Then team X gets 20 consecutive walks on 80 pitches right down the middle.
Would the principles of sportsmanship demand that the other officials and players honor the decision of the umpire? The official rules of baseball give him the absolute authority to declare whether or not each pitch went through the strike zone, and provide that there can be no legitimate challenge to his rulings. Nonetheless, I would suggest that good sportsmanship would require after awhile that players and officials should seek to undermine him.
If a pitch is down the middle, the first- or third-base umpires should rule that the batter swung at the ball, whether or not he did. The official responsible for calling games on account of weather should announce that there is a rainstorm that makes it impossible to continue the game, even if the sky is perfectly clear. The team which would be favored by the absurd rulings should seek to minimize any benefit received therefrom, and would show good sportsmanship if they were to forfeit the game in preference to receiving a clearly-unjust victory. If either team opts to forfeit, the official scorekeeper should regard the game as having been canceled.
Note that none of those remedies is provided for under the rules of baseball, and many of them would require officials to go against their prescribed duties. Nothing in the rules of baseball allows for a determination that an umpire is just plain unreasonable, and so there would be no particular time when anyone else should decide to take matters into his own hands. Nonetheless, the principles of good sportsmanship would demand that players and officials take action when it becomes clear to them that not only do they believe the home plate umpire is acting unreasonably, but they believe his actions are so patently unreasonable that no reasonable person could believe him to be acting reasonably.
Note that because the Constitution does not give judges' rulings supremacy over the Constitution itself (unlike the rules of baseball, which do give the home plate umpire's rulings supremacy), the threshold for overriding such rulings should perhaps be slightly lower than for overriding the home plate umpire. Any apparent anarchy which might result would be the fault of the judges who issued the unlawful rulings, rather than those who sought to undermine them.