Regardless if you believe is using an animal for meat or not, a shark is not one we should indulge in. For one, these are very dangerous animals to hunt. The lose of life that could possibly be caused by hunting for them would be far more than say hunting elk. Many breads of shark are endangered, so the hunting would be even more outrageous. Certain sharks are known for eating junk found in their hunting areas, so we could not say that perhaps a shark that is to be eaten would have consumed large plastic pieces, or something even more dangerous. Also, the cost of hunting these animals for food would be extremely expensive.
Sharks, and many other ocean animals, are already being over-fished. Their populations are dwindling due to a high demand in the market. Efforts need to be made to fish sustainably and to avoid senseless killings of animals. Taking the fins off a shark and tossing it back in the ocean to die is in no way a good enough reason to kill that shark.
They didn't know that sharks were killed to make a soup? How else would the shark fin get IN the soup in the first place? The alternative would be horrible! But do Koreans know that dogs are killed for bugogi? Or do Americans know that cows were killed to get a steak? Yes. How could you NOT know that!? Now, should it be outlawed internationally? I guess it depends on the shark population and whether or not there are shark farms like cattle, pig and dog farms in other countries.
No, the fact that many Chinese didn't know sharks were killed to make soup does not necessarily mean the practice should be outlawed internationally. A world-wide ban would be appropriate either in cases where an animal was endangered or when the consumption of an animal was dangerous to the public's health. Otherwise, this type of practice should be regulated by individual countries, according to their laws and customs.