I would no more convict a man of the simple decision to go armed about his business than I would convict him of trespass for entering a whites only restroom if he were black.
I do not believe that the passing of a law by some legislature and it's subsequent signature by some governor (or president) relieves me of the responsibility to evaluate the morality of that law.
What else does it mean to be a citizen if not to ride herd on the elected help.
Surely there are methods to attempt change by affecting the legislative process, but just as surely there are environments where it is a practical impossibility to succeed.
To vote one's conscience is a duty, not a privilege. If you ignore the moral implications of a law, you are remiss, in my opinion when serving as a juror.
To refuse to convict, does not set precedent. It is only when citizens refuse to convict in case after case, that it becomes apparent that, despite legislative approval, a particular law is suspect.
All that being said, judges and prosecutors do a pretty good job of weeding out folks who aren't willing to follow the judge's instruction to consider the FACTS and not the law.
Last time I went in, the judge specifically asked if anyone had HEARD ABOUT (not believed in) jury nullification and dumped everyone who raised their hand.