When juries realize the law is stupid and they use common sense, it’s a win for society. Many of our laws were designed simply as revenue streams and to take the power away from citizens.
It's a bad precedent when the govt jails people for committing non-criminal "crimes" that don't infringe upon the life, liberty, or property of others. Jury nullification is a tool to combat the unjust behavior of the govt.
This is our system of checks and balances. Nothing in the constitution says juries have to punish people for bad laws. In fact, a stronger case could be made that prohibition is unconstitutional and the jury is the only party acting right.