This is fairly bad logic it presumes we must either do no evil whatsoever or do however much evil we like because we refuse to do no evil. You could trivially extend it to eating people after all why are we picking which animal its OK to eat? Back in reality we should probable stop eating animals but a world where we do less harm is still better than one where we do more and most of us would race to stop the consumption of 3 children before we would endeavor to save 3 million chickens. The argument goes that the whales are closer to the children than the chickens. Even if you don't think this is fair or reasonable nobody is going to save the chickens and there is political and moral will to save the whales so perhaps be happy with the good that we can do instead of insisting on all or none.