> Wouldn't the democratic way be to petition...

This is also the democratic way, arguably more democratic, it's just probabilistic. Juries are supposed to be randomly sampled from the jurisdiction's population (a kind of democratic process). The ability of a jury to judge the law, and not just the particular crime is a feature, not a bug of the justice system. This is how the system is set up, and it is as legitimate as action through a legislative process.

EDIT: the parent asked a legitimate question in good faith, there is no need to downvote them because you disagree with their implied current understanding of an issue.