OOC: The reason I did not move right to scry and capture is that Jorah did not break any of your laws, broke the laws of Robert Baratheon and Eddard Stark. If he is being a productive member of society in Western Essos there is a case to be made for Viserys leaving him alone. He has hired worse slavers than him.
Before we became involved, Slavery was legal in Essos. You could make the argument that all of the Slavers we conquered were not doing anything illegal at the time. Now that it's against the law, they either stopped, to come into compliance with our law, or they were hung.
Slavery was never legal in Westeros. Jorah broke the law as it was written in a place and time it was illegal and the sentence is the Wall or the Rope. Jorah really should have known better.
Given that we are the rightful King (if one who is not currently occupying our traditional seat) it is completely within our prerogative to execute Westerosi law. Viserys has always been king, legally, the practicalities have just been a bit more complicated.