Divingsinmyblood--what are your views then on taking small sharks out of the water? Eventually, you'll probably have to argue that we shouldn't take any sharks out of the water.
Fundamentally, I somewhat agree, we shouldn't overfish by any means. However, fish and animals are not nearly on the same "level" as humans, just as buildings and cars aren't. So I don't have a problem with fish dying, as long as they aren't being killed just for fun. I think that any fish caught should be eaten, unless it's poisonous. I also don't have a problem with buldings beign demolished, as long as it has a purpose. Setting fires for fun is wrong, just like drag net fishing is wrong. But it's not wrong for me to demolish a house to build a new one, just like it's not fundamentally wrong for this man to catch the fish. (even if it's not the best use of his time

)
At any rate, I think you need to be really careful with threats like "lets go hunting for some fisherman." I understand it was probably in jest, but it can be hard to tell. It would be wise of you to amend your post with something like
[humor] and [/humor]
or

at the end of your threat.
In order to affect the greatest change, you should not threaten people with a speargun. Perhaps you should write a letter to the organization that was having the tournament (wasn't it a tournament for game fish?) or if I'm wrong on that, the fishing boat crew or something, whatever it was, whomever was in charge, etc, and let them know that while it's cool that these guy shad fun, you would have rathered to have seen a news story documenting the catch and then the subsequent release of the animal, or something to that nature.
Think of wedges, they get you to a height gradually. You cannot start by calling for physical harm to a person, you ought to start small and move people over to your side over time, it works much better than extreme demands and threats.
Again, it was probably all in jest, and I suggest you amend your post to accurately reflect your intentions, or ask a moderator to move this entire thread to "fun and games" where humor is more easily appreciated. Until you do something, you will have people who take what you said at face value (I know becuase I say a whole tonne of stupid things all the time and have to apologize and amend posts) and get upset with you, when otherwise they might have agreed with you.