I think this really comes down to a shared definition of griefing. Where does playing the game stop and griefing begin? At a totally theoretical level - griefing feels like playing the game not in the spirit that was intended by the design.
Competitive behaviour on a PvP world, searching for any angle and opportunity to compete, feels like fair game. Bend the game for your advantage. But doing the same things on a non-PvP world to players who have actively opted out of this level of competition would feel unwanted.
So without talking about specifics, if your gaming isn't nasty or obnoxious then I don't think there would be any problem.
- Players who remove their beacons will be opting to give up their land - feels fair game.
- Unclaimed land can be claimed by other players or it will get refreshed by the world generator.
- If you want to pillage then you'll be more interested in the generated dungeons and monuments filled with protectors. These will offer the main challenge and rewards. Or if you're feeling really bold - go take on some of the titans . Classic - pick on someone your own size