This started out to be a comment to SayUncle's post on jury nullication but ended up being a blog post instead.
We have a legal system. Not a justice system. I'm not saying this is avoidable, it's just a statement of the facts.
IMHO our legal system is an approximation to a justice system. That given I fully agree there are lots of laws that need to be eliminated or changed. There is more than one path to that end. There is the obvious path through the legislature and is to be preferred but there are alternatives as well.
One alternate path to legal change is jury nullification. After I was on a jury I talked to the prosecutor about this very issue. Read about it here if you want.
Another path that is less palatable is demanding the vigorous enforcement of unjust laws. If fornication is against the law (it was in Idaho the last time I looked), so demand the unmarried child of the prosecutor, or police chief living with there significant other be prosecuted. Make a big stink about it such that it gets in the papers. Make it such that the law enforcement community of that jurisdiction comes out and literally says, "We will not prosecute cases under this law." The law is, in essence, stricken from the books in that jurisdiction. The down side is that if you can't find someone that is "conviction proof" to make the stink over you might end up with lot of "innocent" people convicted. If you can fill the jails with "innocent" people the legislature will fix the problem because of the population at large will demand it. But, in essence, you will be creating martyrs for your cause. You should get their permission to be martyred before doing so. It is considered very rude to martyr someone without their permission and could result in their own version of justice being visited upon you.