Bazza,
Some of what you're talking about, those examples, are out of ignorance on the part of the participant- old mate probably wasn't even thinking about sharks swimming out there with his dog. Some of it, too, is up to the individual. If you're talking placing others' lives at risk if/when sh%t hits the fan, then you won't be doing too many things that raise a hair or two. Crossing a bar, for one. Even fishing offshore. Both of these can place rescuers' lives at risk. Would you not do that?
I would argue that spearing Amity isn't one of those activities, anyway. If Mr Chompie comes and grabs a spearo, then there won't be time for rescues to occur. If the spearo survives, he/she will be back to shore before rendering any help. No other lives at risk. If you look at the stats, you'll also agree that the spearo's life isn't at risk, either. Chances are so small they're not worth contemplating.
Cuzza