Basically, it boils down to cold logic. If we are going to care about the suffering of other humans then logically we should care about the suffering of non-humans too. It is the heartless exploiter of animals, not the animal protectionist, who is being irrational, showing a sentimental tendency to put his own species on a pedestal. We all, thank goodness, feel a natural spark of sympathy for the sufferings of others. We need to catch that spark and fan it into a fire of rational and universal compassion. ~Richard Ryder
Quote from Immanuel Kant, a German philosopher, who is widely considered to be a central figure of modern philosophy.