According to the article “ Pro-whaling nations expected the moratorium to be temporary, until consensus could be reached on sustainable catch quotas.” If this fishing is truly sustainable and doesn’t threaten the whales with extinction there shouldn’t be a problem. Why should whales get protection that pigs, cows, and other animals don’t?
An adult sperm whale weighs over 100 tons and eats about a ton a day. Do you not see the practical implications of that with regards to irreversible damage?
Edit: missed the sustainable part of your post. Whaling afaik can't be sustainable because the demand in Japan is high enough that whale populations simply can't replenish fast enough. They have a very slow reproductive and nurturing cycle.