There is many invasive that need to be killed. Such as http://ocean.si.edu/ocean-news/5-invasive-species-you-should-know such as the sea walnut, killer algae, green crab, Veined Rapa Whelk, and Zebra Mussel.
Whales have been on earth about 50 million year. And now we decide to kill the whales. We have not been on earth as long whales. At first it was a need because it is a food source.
This activity for others is not a need for food it is a need for something