Is jury nullification the ultimate trump card? From what little I know about it, it seems that if enough people in a community knew about it, they could 100% control what crimes are punished in that community. On face value, that makes a sort of sense intuitively, but obviously it has to be balanced against crimes that are in principle clearly wrong, despite what a local community believes.
The jury is an old form of democracy. The king/government can make what laws they like, but it needs to have enough popular support that a jury will freely choose to convict according to it.
Of course, like all forms of democracy, the outcomes don't always agree with your or my sense of justice.
> it has to be balanced against crimes that are in principle clearly wrong
In this system, whoever gets to decide what is "clearly wrong" has the real power.