And yet apparently sabotage on the high seas makes one a pirate (or "enemy of humanity", if you like):
http://www.internationalskeptics.com/forums/showthread.php?postid=5499979#post5499979
Actions have meanings, too. Given Sea Shepherd's stated mission, and their established MO, what is it that you believe entitles them to set the terms of engagement or determine the limits of escalation?
Although, the more I think about it, I'm not sure what your problem is, even by your own definitions. So the Sea Shepherd is a saboteur organization. Alright, fine: You're not arguing that saboteurs should be exempt from sabotage themselves, are you? And you're not arguing that the same laws of the sea that give Sea Shepherd the privilege of committing acts of sabotage prohibit their intended victims from engaging in sabotage as well, are you? So then, consider sinking the
Ady Gil as an act of sabotage, every bit as legitimate as any act of sabotage ever committed by Sea Shepherd.
As for risk to human life, Sea Shepherd puts lives at risk with every act of sabotage they commit. Sure, they take precautions, but precautions don't eliminate risk. Policemen sometimes shoot innocent people. Firefighters don't always come out of the burning buildings they rush into. Warfare includes collateral damage and friendly fire incidents.
Sea Shepherd has chosen to play a risky game, and they've forced other people to play the game with them. Why should those people play that game by Sea Shepherd's rules? Why should those people--who would prefer not to play Sea Shepherd's game at all--keep the risk level within Sea Shepherd's comfort zone, or keep attrition to a level Sea Shepherd can sustain? Why should Sea Shepherd be entitled to sail the seas, proclaiming, "this much sabotage, and no more"?