I really feel this game needs 3 modes of play...
Arena (but this mode needs to be tweaked)
Pirate Adventure; PVP, exactly how it is right now for Adventure, except better loot, high risk, high reward.
Casual Adventure; No PVP, you can't kill other players or damage their ship. You can still have alliances and share loot. You can still battle together all the regular PVE, just not other players. But, the loot is less. Low risk, low reward.