I think Dadano has the essential point, and Vulcan is just being argumentative to try to make a point.
I personally think that there is a huge difference in intellectual capacity between cows bred for meat and dolphins, and that means killing and eating cows is NOT the same as killing and eating dolphins (or any other more intelligent critter). Plus, cows and most other food animals are managed and slaughtered in the most "humane" way possible while this method of harvesting dolphins doesn't seem to have any consideration for minimizing the suffering of the animal. The way they're taking those dolphins is unnecessarily painful and cruel l in my opinion, and the fact that dolphins are most likely more intelligent than dogs (which we consider to be too intelligent to eat for food) makes this sort of thing open to questions of morality.
If they MUST be eaten due to lack of a less intelligent source of food, then I think it ought to be done in a less torturous fashion. We are after all at the top of the food chain, and if a human NEEDS food then anything below us on the food chain is fair game. But even slaughtering hogs where they bleed them out alive is done in what seems to be about 1/100th the time with significantly less pain and suffering.
I think one other thing that bugs people about this is that they don't NEED those dolphins to survive. If they'd relax their trade restrictions on protein imports, they could get all the cheap beef and other meat they could possibly want. Some of the arguments in favor of dolphin hunting like this sound a whole lot like the arguments that justify killing endangered elephants for their ivory... It's all "we're humans so we're in charge, and you're a pansy for letting a little blood bother you". Harumph... Legit slaughtering to satisfy needs is just fine, but I think it ought to be done in as humane a fashion as possible. Putting intelligent animals into a panic for hours followed by slowly suffocating them over another few hours just doesn't seem right to me. We don't even do that to rapists and child molesters...