Mahi mahi is also knows as dolphin, but it's not literally a dolphin. Very ugly fish if I say so myself. Very tasty, too.
http://www.torpedotours.com/images/mahi.jpg
To me, it's wrong because they are so intelligent. But sort of not. It's like, what kind of person could kill an elephant or a monkey? Not one that I'd like to meet. Then again, pigs are more intelligent than dogs, yet we don't eat dogs and pigs aren't man's best friend. Except truffle farmers (naturally.) Morally? I don't have a problem with it....from an anthropological perspective I guess. Practically? They are too cute and smart to kill. That's the reason I can't eat lamb or veal. I don't have a moral problem with it, I just can't stand the thought of eating something so cute and innocent. It's interesting that I just said the word "innocent." Look at how I just anthropomorphized the animals, when in fact they are no better or worse than any other animal. Except for the sloth, of course. They're evil, you know.
Reminds me of a joke I heard on TV. It's something like A vegetarian is helping a dolphin trapped in a net, and while doting over the dolphin he keeps saying "Get out of the way, you stupid tuna!!!"
Look at India. The cow is sacred there, and it's just livestock here. That is a perfect analogy between the views of almost everyone in the west and the people who do this in Japan. IIRC, The Japanese also kill whales in the name of "research" but I think they end up being consumed and/or only being killed for their ambergris. Some loophole I saw on some documentary that I'm FAR too lazy to research right now. Technically, killing a dolphin is no different than killing a cow, but to us it seems unthinkable because of differences in our culture and theres.
All of the above is assuming no endangered/threatened species are being killed. I'm, of course, strongly opposed to that.