Hmmmm, this might be a cultural thing, but here in Australia if there was a shark in the water and he was attacking someone then HELL YES I would get into the water to help. And any of my mates would do that, too. In fact I have been attacked by a shark, and got away with no more than a huge fright - when this happened a couple of my mates then even went after the shark with their boards and started whacking it. Albeit - it's not as crazy as it sounds, it was a young shark and quite small.
Most people that I know here would not hesitate to get into the water to help anyone fend off a shark, you'd help anyone you'd see fend off a vicious dog, too, wouldn't you?
hardgainer (pump)