I'm disappointed there's no option depending on traits/abilities on your race.
I haven't play the Festron Hunt but the Ravenous ability seems like a start.
I really want to purge, eat them as food, kill for exp, use them as target practice (increase soldering).
If citizens you don't want get purged, they can be refugees and will try to go to another civilization till one accepts them. If no one accepts them they can move to an uncolonized planet and form a new faction.