It's a tricky subject though. In the US, it's been used to bring judgements closer to what we consider legal today, like refusing to convict on the Fugitive Slave Act or alcohol control laws during prohibition. But there are also cases of all white juries refusing to convict for hate crimes despite obvious evidence.
https://en.wikipedia.org/wiki/Jury_nullification_in_the_Unit...
The point of the discussion, that we're keeping a bunch of people locked up for violating laws that we have recently decided were unjust, isn't relativistic at all. In a just society those people would be freed immediately.
One might stipulate that whether marijuana should be illegal isn't an absolute that can never change.
But if it is in accordance with our values that it should be legal now, and this is our best attempt at instituting just laws, then leaving people in jail for reasons we don't currently think are valid is relatively worse than any arbitrary rule about drugs.
Just because you don't know for sure what is truly and absolutely right doesn't mean you can't stop doing things you know are truly and absolutely wrong.
Side note: I love your username :-)