If we are defined by reason and morality, then reason and morality must define our choices, even when animals are concerned. When people say, for example, that they like their veal or hot dogs too much to ever give them up, and yeah it's sad about the farms but that's just the way it is, reason hears in that the voice of gluttony. We can say that what makes a human being human is precisely the ability to understand that the suffering of an animal is more important than the taste of a treat.