First off, you are appealing to instincts which not everyone has. People who work on farms are happy to slaughter animals. A lot of people do not own pets simply because they do not feel any affection towards animals and care more for material objects. Many people do not care about the clubbing of seals. It is human beings of course who perform these clubbing, murder sharks, poach etc. Furthermore, it is irrational that people care about their pets because cows are equally as sentient as animals yet people are happy to eat veal and battery farmed beef and clearly do not care about the cow.  People treat pets as property. They buy and sell them, put them down when they contract illnesses that are too expensive to treat, give them away when they move houses etc. These are things that they certainly wouldn’t do to human beings. If you want to argue according to what humans do instinctively then we instinctively value humans more than animals and are happy to eat and kill animals.  Furthermore, we do not think that using a descriptive claim- what humans feel instinctively- means that you can then make a prescriptive claim – that all sentient beings deserve equal consideration.  In many ways we treat other human beings as only extrinsically valuable. Neo-Malthusians believe we should allow the poor to die of hunger to ensure that the current population does not suffer from the scarcity that arises from overpopulation. Many wars have involved killing lots of people to achieve political aims. Therefore, we often treat humans as extrinsically valuable.