I think you should be able to protect certain areas from griefers. Sure, you can kick, but why let your friend on not knowing what he will do? Why spend all your time administrating if nobody is there? Introducing... Safe-Zones!
You can NOT place or break blocks, but, different than PC Plugins, you can PvP in it, for PvP Arenas and things, but you can't break blocks. It would be impossible to grief, of course! There is a twist however: To prevent random claiming, only the HOST can claim Safe-Zones. This is to prevent griefing with antigrief safezones.