Have you ever heard of jury nullification? Chances are if you're not a part of the liberty movement in the United States, you haven't. However, it was the method the framers of the Constitution provided to set up the last "check and balance" to the system.
Basically, jury nullification states that even if the jury is completely convinced that the defendant is guilty of breaking the law, if they do not believe the law to be a good law, they can still find the defendant innocent.
In this manner, stupid laws that everyone knows are stupid could NOT get enforced. However, not only is this not explained to most jurists, in many jurisdictions the Judge makes it a point to say that the jurists have to merely apply the law, as the Judge has explained it, to the facts of the case as the jury finds it.
Now, any decent attorney would probably find reason to throw me off of a jury long before I became impaneled (I tend to distrust those with power -- especially police officers -- and will NOT enforce a victimless crime even with a "smoking gun"), but if I were to ever make it to a jury, it would be my duty as I see it to ensure that all members of the jury were aware of their legal power to nullify the law if they believe it to be a bad one.
Meanwhile, I do what I can to explain the concept to people if the topic happens to come up. The more of the populace aware of the idea of jury nullification, the better off we're likely to be as a country. Jury nullification alone will probably not get us where we need to go, but it's certainly a step in the right direction.