Here is what I would like to see. - There should be key places around the world/galaxy that are safezones, and no body can fight each other. This could be main quest locations or trading centers. - After that there can be zones where different factions can fight each other. But to avoid shooting everything you see, you could do something like this. Players have Hostility Level. Your level increases and decreases based on how you play. It would influence the amount of experience you gain by killing another player. How exactly this would work without flaws... I don't know.