Don't make the design oppositional, polarized and stereotypical. Not all Minmatar want to free slaves, not all Amarr want to enslave people. Not all slaves are Minmatar, not all slavers are Amarr. Not all Amarr Empire loyalists support slavery, not all Republic adherents want to abolish slavery. Don't force an RP angle on anyone.
Merdaneth has probably freed far more slaves than any 'freedom fighter', I would highly frown on any design that would force me to have good Minmatar standings or be forced to create only Minmatar freed slaves.
Also, there seems to be no room for Amarr Empire action against illegal slavers. Once again, my character regularly hunts down and brings illegal slavers to justice. By just making any enslavement considered positive to the Amarr Empire, you are stereotypicalizing the situation, reducing breadth of gameplay.
Some people in Amarr Faction don't use slaves because they are opposed to slavery. Some people in Amarr Faction don't use slaves because they are actually spies for the Republic. To have them 'drop slaves' would be forcing a certain RP perspective on them. I very set against that.
Standings adjustments: no. It will be gamed.