That's a very good question. We know from Scripture those who don't repent will be condemned, but that is not because God doesn't offer forgiveness to them, but because they choose not to accept it. God still shows some kind of favor to even the unrepentant, as they are not in hell this very moment.

That being said, we are told to forgive because God first forgave us (Ephesians 4:32), and are even warned that if we don't forgive others, God won't forgive us (Matthew 6:14-15). Were not given any qualifiers there: nothing about brothers, repentance, etc. And just like with God, people aren't required to appreciate or accept our forgiveness; their lives just aren't riding on their decision regarding the latter.

Watermelon felon will be going in my repertoire

I'd say forgiveness is for both the victim and the perpetrator. It's an opportunity for us to show the world that we follow the One Who offers grace and forgiveness to all. Just like it was for us, it is a gift to the recipient, an act of love.

As for people still bringing up slavery, it's not about a lack of forgiveness, but a manipulation by politicians to foment entitlement masked with a misplaced sense of justice. No one needs to forgive anyone else for what their ancestors did, especially while ignoring the misdeeds of their own ancestors. The first freed men overcame through faith and moral strength, not through plans for retribution, just like the first Christians did.